算法（Algorithms）第4版 练习 1.5.23

package com.qiusongde;

import edu.princeton.cs.algs4.StdOut;

public class Exercise1523 {

    public static void main(String[] args) {

        int T = Integer.parseInt(args[0]);
        int[] edgesQF = new int[T];
        int[] edgesQU = new int[T];

        for(int N = 250; true; N += N) {

            double timeQF = ErdosRenyi.timeTrialForQF(T, N, edgesQF);
            double timeQU = ErdosRenyi.timeTrialForQU(T, N, edgesQU);

            double meanQFConnect = ErdosRenyi.mean(edgesQF);
            double meanQUconnect = ErdosRenyi.mean(edgesQU);

            StdOut.printf("%6d %7.1f %7.1f %7.1f %7.1f\n", N, meanQFConnect, timeQF, meanQUconnect, timeQU);

        }

    }

}

package com.qiusongde;

import edu.princeton.cs.algs4.StdOut;
import edu.princeton.cs.algs4.StdRandom;
import edu.princeton.cs.algs4.StdStats;
import edu.princeton.cs.algs4.UF;
import edu.princeton.cs.algs4.WeightedQuickUnionUF;

public class ErdosRenyi {

    public static int countByUF(int N) {

        int edges = 0;
        UF uf = new UF(N);

        while (uf.count() > 1) {
            int i = StdRandom.uniform(N);
            int j = StdRandom.uniform(N);
            uf.union(i, j);
            edges++;
        }

        return edges;

    }

    public static int countByQF(int N) {

        int edges = 0;
        UFQuickFind uf = new UFQuickFind(N);

        while (uf.count() > 1) {
            int i = StdRandom.uniform(N);
            int j = StdRandom.uniform(N);
            uf.union(i, j);
            edges++;
        }

        return edges;

    }

    public static int countByWeiQUPathCom(int N) {

        int edges = 0;
        UFWQuickUnionPathCom uf = new UFWQuickUnionPathCom(N);

        while (uf.count() > 1) {
            int i = StdRandom.uniform(N);
            int j = StdRandom.uniform(N);
            uf.union(i, j);
            edges++;
        }

        return edges;

    }

    public static int countByQU(int N) {

        int edges = 0;
        UFQuickUnion uf = new UFQuickUnion(N);

        while (uf.count() > 1) {
            int i = StdRandom.uniform(N);
            int j = StdRandom.uniform(N);
            uf.union(i, j);
            edges++;
        }

        return edges;

    }

    public static int countByWeiQU(int N) {

        int edges = 0;
        WeightedQuickUnionUF uf = new WeightedQuickUnionUF(N);

        while (uf.count() > 1) {
            int i = StdRandom.uniform(N);
            int j = StdRandom.uniform(N);
            uf.union(i, j);
            edges++;
        }

        return edges;

    }

    public static double timeTrialForQF(int T, int N, int[] edges) {

        Stopwatch timer  = new Stopwatch();

        // repeat the experiment T times
        for (int t = 0; t < T; t++) {
            edges[t] = ErdosRenyi.countByQF(N);
        }

        return timer.elapsedTime();

    }

    public static double timeTrialForWeiQU(int T, int N, int[] edges) {

        Stopwatch timer  = new Stopwatch();

        // repeat the experiment T times
        for (int t = 0; t < T; t++) {
            edges[t] = ErdosRenyi.countByWeiQU(N);
        }

        return timer.elapsedTime();

    }

    public static double timeTrialForQU(int T, int N, int[] edges) {

        Stopwatch timer  = new Stopwatch();

        // repeat the experiment T times
        for (int t = 0; t < T; t++) {
            edges[t] = ErdosRenyi.countByQU(N);
        }

        return timer.elapsedTime();

    }

    public static double mean(int[] edges) {
        return StdStats.mean(edges);
    }

    public static void main(String[] args) {

             int n = Integer.parseInt(args[0]);          // number of vertices
            int trials = Integer.parseInt(args[1]);     // number of trials
            int[] edges = new int[trials];

            // repeat the experiment trials times
            for (int t = 0; t < trials; t++) {
                edges[t] = countByUF(n);
            }

            // report statistics
            StdOut.println("1/2 n ln n = " + 0.5 * n * Math.log(n));
            StdOut.println("mean       = " + StdStats.mean(edges));
            StdOut.println("stddev     = " + StdStats.stddev(edges));
    }

}

package com.qiusongde;

public class Stopwatch {

    private final long start;

    public Stopwatch() {
        start = System.currentTimeMillis();
    }

    public double elapsedTime() {
        long now = System.currentTimeMillis();
        return (now - start) / 1000.0;
    }

}

结果：

   250   854.0     0.0   738.0     0.0
   500  1554.0     0.0  1832.0     0.0
  1000  3291.0     0.0  3616.0     0.0
  2000 10467.0     0.0  7477.0     0.0
  4000 17488.0     0.0 15609.0     0.0
  8000 41016.0     0.0 37187.0     0.1
 16000 70888.0     0.2 74066.0     0.8
 32000 166090.0     0.9 153517.0     4.1
 64000 370711.0     3.5 333206.0    19.4
128000 698381.0    16.3 884453.0   233.5

比较奇怪的是Quick-union的运行时间比Quick-find的还要久。