001package algs15;
002import java.util.Arrays;
003import stdlib.*;
004/* **************************************************************************
005 *  Compilation:  javac WeightedQuickUnionHalvingUF.java
006 *  Execution:  java WeightedQuickUnionHalvingUF < input.txt
007 *  Dependencies: StdIn.java StdOut.java
008 *
009 *  Weighted quick-union with path compression via halving.
010 *
011 ****************************************************************************/
012
013public class XWeightedHalvingUF implements UF {
014        private int[] id;    // id[i] = parent of i
015        private int[] sz;    // sz[i] = number of objects in subtree rooted at i
016        private int count;   // number of components
017
018        // instantiate N isolated components 0 through N-1
019        public XWeightedHalvingUF(int N) {
020                count = N;
021                id = new int[N];
022                sz = new int[N];
023                for (int i = 0; i < N; i++) {
024                        id[i] = i;
025                        sz[i] = 1;
026                }
027        }
028
029        // return number of connected components
030        public int count() {
031                return count;
032        }
033
034        // return component identifier for component containing p
035        public int find(int p) {
036                int root = p;
037                while (root != id[root]) {
038                        if (id[root] != id[id[root]]) {
039                                id[root] = id[id[root]];    // path compression by halving
040                                if (TestUF.SHOW_COMPRESSION_STEPS) { StdOut.format("%2d %2d> %2d%s\n", root, id[root], this.count(), this); toGraphviz(); }
041                        }
042                        root = id[root];
043                }
044                return root;
045        }
046        // return component identifier for component containing p
047        public int findSimple(int p) {
048                int root = p;
049                while (root != id[root]) {
050                        id[root] = id[id[root]];
051                        root = id[root];
052                }
053                return root;
054        }
055
056        // are elements p and q in the same component?
057        public boolean connected(int p, int q) {
058                return find(p) == find(q);
059        }
060
061        // merge components containing p and q, making smaller root point to larger one
062        public void union(int p, int q) {
063                int pid = find(p);
064                int qid = find(q);
065                if (pid == qid) return;
066                // in the case of a tie, p is the champion
067                if   (sz[pid] < sz[qid]) { id[pid] = qid; sz[qid] += sz[pid]; }
068                else                     { id[qid] = pid; sz[pid] += sz[qid]; }
069                count--;
070        }
071
072        public String toString() { return Arrays.toString (id); }
073        public void toGraphviz() { GraphvizBuilder.ufToFile (id); }
074
075        public static void main(String[] args) {
076                boolean print = true;
077                StdIn.fromFile ("data/tinyUF.txt"); 
078                //StdIn.fromFile ("data/mediumUF.txt"); print = false;
079                //StdIn.fromFile ("data/largeUF.txt"); print = false;
080
081                int N = StdIn.readInt();
082                XWeightedHalvingUF uf = new XWeightedHalvingUF(N);
083                if (print) { uf.toGraphviz(); StdOut.println("   : " + uf); }
084
085                // read in a sequence of pairs of integers (each in the range 0 to N-1),
086                // calling find() for each pair: If the members of the pair are not already
087                // call union() and print the pair.
088                Stopwatch sw = new Stopwatch ();
089                while (!StdIn.isEmpty()) {
090                        int p = StdIn.readInt();
091                        int q = StdIn.readInt();
092                        if (uf.connected(p, q)) continue;
093                        uf.union(p, q);
094                        if (print) { StdOut.println(p + " " + q + ": " + uf); uf.toGraphviz(); }
095                }
096                StdOut.format("XWeightedHalvingUF # components: %d [%f]", uf.count(), sw.elapsedTime ());
097        }
098
099}