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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;
    }
}