1 | // License: GPL. For details, see LICENSE file.
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2 | package org.openstreetmap.josm.data.osm;
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3 |
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4 | import java.util.ArrayDeque;
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5 | import java.util.ArrayList;
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6 | import java.util.Collection;
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7 | import java.util.Collections;
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8 | import java.util.Comparator;
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9 | import java.util.Deque;
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10 | import java.util.HashMap;
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11 | import java.util.HashSet;
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12 | import java.util.LinkedHashMap;
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13 | import java.util.LinkedHashSet;
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14 | import java.util.List;
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15 | import java.util.Map;
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16 | import java.util.Map.Entry;
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17 | import java.util.Optional;
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18 | import java.util.Set;
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19 | import java.util.TreeMap;
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20 | import java.util.stream.Collectors;
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21 | import java.util.stream.Stream;
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22 |
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23 | import org.openstreetmap.josm.tools.Pair;
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24 | import org.openstreetmap.josm.tools.Utils;
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25 |
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26 | /**
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27 | * A directed or undirected graph of nodes. Nodes are connected via edges represented by NodePair instances.
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28 | *
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29 | * @since 12463 (extracted from CombineWayAction)
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30 | */
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31 | public class NodeGraph {
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32 |
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33 | /**
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34 | * Builds a list of pair of nodes from the given way.
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35 | * @param way way
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36 | * @param directed if {@code true} each pair of nodes will occur once, in the way nodes order.
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37 | * if {@code false} each pair of nodes will occur twice (the pair and its inverse copy)
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38 | * @return a list of pair of nodes from the given way
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39 | */
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40 | public static List<NodePair> buildNodePairs(Way way, boolean directed) {
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41 | List<NodePair> pairs = new ArrayList<>();
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42 | for (Pair<Node, Node> pair : way.getNodePairs(false)) {
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43 | pairs.add(new NodePair(pair));
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44 | if (!directed) {
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45 | pairs.add(new NodePair(pair).swap());
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46 | }
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47 | }
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48 | return pairs;
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49 | }
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50 |
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51 | /**
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52 | * Builds a list of pair of nodes from the given ways.
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53 | * @param ways ways
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54 | * @param directed if {@code true} each pair of nodes will occur once, in the way nodes order.<br>
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55 | * if {@code false} each pair of nodes will occur twice (the pair and its inverse copy)
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56 | * @return a list of pair of nodes from the given ways
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57 | */
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58 | public static List<NodePair> buildNodePairs(List<Way> ways, boolean directed) {
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59 | List<NodePair> pairs = new ArrayList<>();
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60 | for (Way w : ways) {
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61 | pairs.addAll(buildNodePairs(w, directed));
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62 | }
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63 | return pairs;
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64 | }
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65 |
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66 | /**
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67 | * Builds a new list of pair nodes without the duplicated pairs (including inverse copies).
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68 | * @param pairs existing list of pairs
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69 | * @return a new list of pair nodes without the duplicated pairs
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70 | */
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71 | public static List<NodePair> eliminateDuplicateNodePairs(List<NodePair> pairs) {
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72 | List<NodePair> cleaned = new ArrayList<>();
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73 | for (NodePair p : pairs) {
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74 | if (!cleaned.contains(p) && !cleaned.contains(p.swap())) {
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75 | cleaned.add(p);
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76 | }
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77 | }
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78 | return cleaned;
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79 | }
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80 |
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81 | /**
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82 | * Create a directed graph from the given node pairs.
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83 | * @param pairs Node pairs to build the graph from
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84 | * @return node graph structure
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85 | */
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86 | public static NodeGraph createDirectedGraphFromNodePairs(List<NodePair> pairs) {
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87 | NodeGraph graph = new NodeGraph();
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88 | for (NodePair pair : pairs) {
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89 | graph.add(pair);
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90 | }
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91 | return graph;
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92 | }
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93 |
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94 | /**
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95 | * Create a directed graph from the given ways.
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96 | * @param ways ways to build the graph from
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97 | * @return node graph structure
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98 | */
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99 | public static NodeGraph createDirectedGraphFromWays(Collection<Way> ways) {
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100 | NodeGraph graph = new NodeGraph();
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101 | for (Way w : ways) {
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102 | graph.add(buildNodePairs(w, true));
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103 | }
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104 | return graph;
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105 | }
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106 |
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107 | /**
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108 | * Create an undirected graph from the given node pairs.
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109 | * @param pairs Node pairs to build the graph from
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110 | * @return node graph structure
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111 | */
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112 | public static NodeGraph createUndirectedGraphFromNodeList(List<NodePair> pairs) {
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113 | NodeGraph graph = new NodeGraph();
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114 | for (NodePair pair : pairs) {
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115 | graph.add(pair);
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116 | graph.add(pair.swap());
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117 | }
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118 | return graph;
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119 | }
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120 |
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121 | /**
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122 | * Create an undirected graph from the given ways, but prevent reversing of all
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123 | * non-new ways by fixing one direction.
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124 | * @param ways Ways to build the graph from
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125 | * @return node graph structure
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126 | * @since 8181
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127 | */
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128 | public static NodeGraph createUndirectedGraphFromNodeWays(Collection<Way> ways) {
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129 | NodeGraph graph = new NodeGraph();
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130 | for (Way w : ways) {
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131 | graph.add(buildNodePairs(w, false));
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132 | }
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133 | return graph;
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134 | }
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135 |
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136 | /**
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137 | * Create a nearly undirected graph from the given ways, but prevent reversing of all
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138 | * non-new ways by fixing one direction.
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139 | * The first new way gives the direction of the graph.
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140 | * @param ways Ways to build the graph from
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141 | * @return node graph structure
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142 | */
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143 | public static NodeGraph createNearlyUndirectedGraphFromNodeWays(Collection<Way> ways) {
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144 | boolean dir = true;
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145 | NodeGraph graph = new NodeGraph();
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146 | for (Way w : ways) {
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147 | if (!w.isNew()) {
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148 | /* let the first non-new way give the direction (see #5880) */
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149 | graph.add(buildNodePairs(w, dir));
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150 | dir = false;
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151 | } else {
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152 | graph.add(buildNodePairs(w, false));
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153 | }
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154 | }
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155 | return graph;
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156 | }
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157 |
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158 | private final Set<NodePair> edges;
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159 | private int numUndirectedEdges;
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160 | /** The number of edges that were added. */
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161 | private int addedEdges;
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162 | private final Map<Node, List<NodePair>> successors = new LinkedHashMap<>();
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163 | private final Map<Node, List<NodePair>> predecessors = new LinkedHashMap<>();
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164 |
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165 | /**
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166 | * Constructs a lookup table from the existing edges in the graph to enable efficient querying.
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167 | * This method creates a map where each node is associated with a list of nodes that are directly connected to it.
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168 | *
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169 | * @return A map representing the graph structure, where nodes are keys, and values are their direct successors.
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170 | * @since 19062
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171 | */
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172 | public Map<Node, List<Node>> createMap() {
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173 | final Map<Node, List<Node>> result = new HashMap<>(Utils.hashMapInitialCapacity(edges.size()));
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174 |
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175 | for (NodePair edge : edges) {
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176 | result.computeIfAbsent(edge.getA(), k -> new ArrayList<>()).add(edge.getB());
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177 | }
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178 |
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179 | return result;
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180 | }
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181 |
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182 | /**
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183 | * See {@link #prepare()}
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184 | */
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185 | protected void rememberSuccessor(NodePair pair) {
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186 | List<NodePair> l = successors.computeIfAbsent(pair.getA(), k -> new ArrayList<>());
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187 | if (!l.contains(pair)) {
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188 | l.add(pair);
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189 | }
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190 | }
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191 |
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192 | /**
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193 | * See {@link #prepare()}
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194 | */
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195 | protected void rememberPredecessors(NodePair pair) {
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196 | List<NodePair> l = predecessors.computeIfAbsent(pair.getB(), k -> new ArrayList<>());
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197 | if (!l.contains(pair)) {
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198 | l.add(pair);
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199 | }
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200 | }
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201 |
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202 | /**
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203 | * Replies true if {@code n} is a terminal node of the graph. Internal variables should be initialized first.
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204 | * @param n Node to check
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205 | * @return {@code true} if it is a terminal node
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206 | * @see #prepare()
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207 | */
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208 | protected boolean isTerminalNode(Node n) {
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209 | if (successors.get(n) == null) return false;
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210 | if (successors.get(n).size() != 1) return false;
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211 | if (predecessors.get(n) == null) return true;
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212 | if (predecessors.get(n).size() == 1) {
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213 | NodePair p1 = successors.get(n).get(0);
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214 | NodePair p2 = predecessors.get(n).get(0);
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215 | return p1.equals(p2.swap());
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216 | }
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217 | return false;
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218 | }
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219 |
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220 | protected void prepare() {
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221 | Set<NodePair> undirectedEdges = new LinkedHashSet<>();
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222 | successors.clear();
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223 | predecessors.clear();
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224 |
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225 | for (NodePair pair : edges) {
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226 | if (!undirectedEdges.contains(pair) && !undirectedEdges.contains(pair.swap())) {
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227 | undirectedEdges.add(pair);
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228 | }
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229 | rememberSuccessor(pair);
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230 | rememberPredecessors(pair);
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231 | }
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232 | numUndirectedEdges = undirectedEdges.size();
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233 | }
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234 |
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235 | /**
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236 | * Constructs a new {@code NodeGraph}.
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237 | */
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238 | public NodeGraph() {
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239 | edges = new LinkedHashSet<>();
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240 | }
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241 |
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242 | /**
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243 | * Add a node pair.
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244 | * @param pair node pair
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245 | */
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246 | public void add(NodePair pair) {
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247 | addedEdges++;
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248 | edges.add(pair);
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249 | }
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250 |
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251 | /**
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252 | * Add a list of node pairs.
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253 | * @param pairs collection of node pairs
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254 | */
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255 | public void add(Iterable<NodePair> pairs) {
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256 | for (NodePair pair : pairs) {
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257 | add(pair);
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258 | }
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259 | }
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260 |
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261 | /**
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262 | * Return the edges containing the node pairs of the graph.
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263 | * @return the edges containing the node pairs of the graph
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264 | */
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265 | public Collection<NodePair> getEdges() {
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266 | return Collections.unmodifiableSet(edges);
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267 | }
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268 |
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269 | /**
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270 | * Return the terminal nodes of the graph.
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271 | * @return the terminal nodes of the graph
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272 | */
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273 | protected Set<Node> getTerminalNodes() {
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274 | return getNodes().stream().filter(this::isTerminalNode).collect(Collectors.toCollection(LinkedHashSet::new));
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275 | }
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276 |
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277 | private List<NodePair> getConnectedPairs(Node node) {
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278 | List<NodePair> connected = new ArrayList<>();
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279 | connected.addAll(Optional.ofNullable(successors.get(node)).orElseGet(Collections::emptyList));
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280 | connected.addAll(Optional.ofNullable(predecessors.get(node)).orElseGet(Collections::emptyList));
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281 | return connected;
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282 | }
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283 |
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284 | protected List<NodePair> getOutboundPairs(NodePair pair) {
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285 | return getOutboundPairs(pair.getB());
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286 | }
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287 |
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288 | protected List<NodePair> getOutboundPairs(Node node) {
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289 | return Optional.ofNullable(successors.get(node)).orElseGet(Collections::emptyList);
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290 | }
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291 |
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292 | /**
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293 | * Return the graph's nodes.
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294 | * @return the graph's nodes
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295 | */
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296 | public Collection<Node> getNodes() {
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297 | Set<Node> nodes = new LinkedHashSet<>(2 * edges.size());
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298 | for (NodePair pair : edges) {
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299 | nodes.add(pair.getA());
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300 | nodes.add(pair.getB());
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301 | }
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302 | return nodes;
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303 | }
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304 |
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305 | protected boolean isSpanningWay(Collection<NodePair> way) {
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306 | return numUndirectedEdges == way.size();
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307 | }
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308 |
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309 | protected List<Node> buildPathFromNodePairs(Deque<NodePair> path) {
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310 | return Stream.concat(path.stream().map(NodePair::getA), Stream.of(path.peekLast().getB()))
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311 | .collect(Collectors.toList());
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312 | }
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313 |
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314 | /**
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315 | * Tries to find a spanning path starting from node {@code startNode}.
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316 | * <p>
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317 | * Traverses the path in depth-first order.
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318 | *
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319 | * @param startNode the start node
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320 | * @return the spanning path; empty list if no path is found
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321 | */
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322 | protected List<Node> buildSpanningPath(Node startNode) {
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323 | if (startNode != null) {
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324 | Deque<NodePair> path = new ArrayDeque<>();
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325 | Set<NodePair> dupCheck = new HashSet<>();
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326 | Deque<NodePair> nextPairs = new ArrayDeque<>(getOutboundPairs(startNode));
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327 | while (!nextPairs.isEmpty()) {
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328 | NodePair cur = nextPairs.removeLast();
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329 | if (!dupCheck.contains(cur) && !dupCheck.contains(cur.swap())) {
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330 | while (!path.isEmpty() && !path.peekLast().isPredecessorOf(cur)) {
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331 | dupCheck.remove(path.removeLast());
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332 | }
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333 | path.addLast(cur);
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334 | dupCheck.add(cur);
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335 | if (isSpanningWay(path))
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336 | return buildPathFromNodePairs(path);
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337 | nextPairs.addAll(getOutboundPairs(path.peekLast()));
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338 | }
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339 | }
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340 | }
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341 | return Collections.emptyList();
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342 | }
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343 |
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344 | /**
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345 | * Tries to find a path through the graph which visits each edge (i.e.
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346 | * the segment of a way) exactly once.<p>
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347 | * <b>Note that duplicated edges are removed first!</b>
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348 | *
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349 | * @return the path; {@code null}, if no path was found
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350 | */
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351 | public List<Node> buildSpanningPath() {
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352 | prepare();
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353 | if (numUndirectedEdges > 0 && isConnected()) {
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354 | // Try to find a path from each "terminal node", i.e. from a
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355 | // node which is connected by exactly one undirected edge (or
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356 | // two directed edges in the opposite direction) to the graph. A
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357 | // graph built up from way segments is likely to include such
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358 | // nodes, unless the edges build one or more closed rings.
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359 | // We order the nodes to start with the best candidates, but
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360 | // it might take very long if there is no valid path as we iterate over all nodes
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361 | // to find out.
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362 | Set<Node> nodes = getTerminalNodes();
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363 | nodes = nodes.isEmpty() ? getMostFrequentVisitedNodesFirst() : nodes;
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364 | return nodes.stream()
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365 | .map(this::buildSpanningPath)
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366 | .filter(path -> !path.isEmpty())
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367 | .findFirst().orElse(null);
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368 | }
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369 | return null;
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370 | }
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371 |
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372 | /**
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373 | * Tries to find a path through the graph which visits each edge (i.e.
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374 | * the segment of a way) exactly once. If the graph was build from overlapping
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375 | * ways duplicate edges were removed already. This method will return null if
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376 | * any duplicated edge was removed.
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377 | *
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378 | * @return List of nodes that build the path; an empty list if no path or duplicated edges were found
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379 | * @since 15573 (return value not null)
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380 | */
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381 | public List<Node> buildSpanningPathNoRemove() {
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382 | List<Node> path = null;
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383 | if (edges.size() == addedEdges)
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384 | path = buildSpanningPath();
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385 | return path == null ? Collections.emptyList() : path;
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386 | }
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387 |
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388 | /**
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389 | * Find out if the graph is connected.
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390 | * @return {@code true} if it is connected
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391 | */
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392 | private boolean isConnected() {
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393 | Collection<Node> nodes = getNodes();
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394 | if (nodes.isEmpty())
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395 | return false;
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396 | Deque<Node> toVisit = new ArrayDeque<>();
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397 | HashSet<Node> visited = new HashSet<>();
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398 | toVisit.add(nodes.iterator().next());
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399 | while (!toVisit.isEmpty()) {
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400 | Node n = toVisit.pop();
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401 | if (!visited.contains(n)) {
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402 | for (NodePair pair : getConnectedPairs(n)) {
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403 | if (n != pair.getA())
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404 | toVisit.addLast(pair.getA());
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405 | if (n != pair.getB())
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406 | toVisit.addLast(pair.getB());
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407 | }
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408 | visited.add(n);
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409 | }
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410 | }
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411 | return nodes.size() == visited.size();
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412 | }
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413 |
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414 | /**
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415 | * Sort the nodes by number of appearances in the edges.
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416 | * @return set of nodes which can be start nodes in a spanning way
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417 | */
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418 | private Set<Node> getMostFrequentVisitedNodesFirst() {
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419 | if (edges.isEmpty())
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420 | return Collections.emptySet();
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421 | // count the appearance of nodes in edges
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422 | Map<Node, Integer> counters = new HashMap<>();
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423 | for (NodePair pair : edges) {
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424 | Integer c = counters.get(pair.getA());
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425 | counters.put(pair.getA(), c == null ? 1 : c + 1);
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426 | c = counters.get(pair.getB());
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427 | counters.put(pair.getB(), c == null ? 1 : c + 1);
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428 | }
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429 | // group by counters
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430 | TreeMap<Integer, Set<Node>> sortedMap = new TreeMap<>(Comparator.reverseOrder());
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431 | for (Entry<Node, Integer> e : counters.entrySet()) {
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432 | sortedMap.computeIfAbsent(e.getValue(), x -> new LinkedHashSet<>()).add(e.getKey());
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433 | }
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434 | LinkedHashSet<Node> result = new LinkedHashSet<>();
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435 | for (Entry<Integer, Set<Node>> e : sortedMap.entrySet()) {
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436 | if (e.getKey() > 4 || result.isEmpty()) {
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437 | result.addAll(e.getValue());
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438 | }
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439 | }
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440 | return Collections.unmodifiableSet(result);
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441 | }
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442 |
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443 | }
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