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package org.graalvm.compiler.graph;

Union-find data structure for Nodes. All operations have an accumulated worst-case complexity of O(a(n)), where a(n) is the inverse of the Ackermann function A(n,n).
/** * Union-find data structure for {@link Node Nodes}. * * All operations have an accumulated worst-case complexity of O(a(n)), where a(n) is the inverse of * the Ackermann function A(n,n). */
public class NodeUnionFind extends NodeIdAccessor { private int[] rank; private int[] parent;
Create a new union-find data structure for a Graph. Initially, all nodes are in their own equivalence set.
/** * Create a new union-find data structure for a {@link Graph}. Initially, all nodes are in their * own equivalence set. */
public NodeUnionFind(Graph graph) { super(graph); rank = new int[graph.nodeIdCount()]; parent = new int[graph.nodeIdCount()]; for (int i = 0; i < parent.length; i++) { parent[i] = i; } }
Merge the equivalence sets of two nodes. After calling this function, find(a) == find(b).
/** * Merge the equivalence sets of two nodes. * * After calling this function, find(a) == find(b). */
public void union(Node a, Node b) { union(getNodeId(a), getNodeId(b)); }
Get a representative element of the equivalence set of a node. This function returns the same representative element for all members of the same equivalence set, i.e., find(a) == find(b) if and only if a and b are in the same set.
/** * Get a representative element of the equivalence set of a node. * * This function returns the same representative element for all members of the same equivalence * set, i.e., find(a) == find(b) if and only if a and b are in the same set. */
public Node find(Node a) { int id = find(getNodeId(a)); return graph.getNode(id); } public boolean equiv(Node a, Node b) { return find(getNodeId(a)) == find(getNodeId(b)); } private void union(int a, int b) { int aRoot = find(a); int bRoot = find(b); if (aRoot != bRoot) { if (rank[aRoot] < rank[bRoot]) { parent[aRoot] = bRoot; } else { parent[bRoot] = aRoot; if (rank[aRoot] == rank[bRoot]) { rank[aRoot]++; } } } } private int find(int a) { int ret = a; while (ret != parent[ret]) { parent[ret] = parent[parent[ret]]; ret = parent[ret]; } return ret; } }