加权路径压缩并查集实现

package algs4;

import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;

import java.io.FileInputStream;
import java.io.InputStream;

/**
 * 并查集
 * Created by blank on 2015-10-15 下午8:56.
 */
public class UF {

    public static void main(String[] args) throws Exception {
        InputStream input = new FileInputStream(Constants.PATH + "largeUF.txt");
        System.setIn(input);
        int N = StdIn.readInt();
        UF uf = new UF(N);
        while (N-- > 0) {
            int p = StdIn.readInt();
            int q = StdIn.readInt();
            if (uf.connected(p, q)) continue;
            uf.union(p, q);
//            StdOut.println(p + " " + q);
        }
        StdOut.println(uf.getCount() + " components");

    }

    private int[] parent;
    private byte[] rank;
    private int count;

    public UF(int n) {
        count = n;
        parent = new int[n];
        rank = new byte[n];
        for (int i = 0; i < n; i++) {
            parent[i] = i;
            rank[i] = 0;
        }
    }

    public int getCount() {
        return count;
    }

    public boolean connected(int p, int q) {
        return find(p) == find(q);
    }

    private int find(int p) {
        while (p != parent[p]) {
            parent[p] = parent[parent[p]];
            p = parent[p];
        }
        return p;
    }

    public void union(int p, int q) {
        int rootP = find(p);
        int rootQ = find(q);
        if (rootP == rootQ) {
            return;
        }
        if (rank[rootP] < rank[rootQ]) {
            parent[rootP] = rootQ;
        } else if (rank[rootP] > rank[rootQ]) {
            parent[rootQ] = rootP;
        } else {
            parent[rootP] = rootQ;
            rank[rootQ]++;
        }
        count--;
    }

}