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算法(Algorithms)第4版 练习 1.5.22

package com.qiusongde;

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

public class Exercise1522 {
    
    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 mean(int[] edges) {
        return StdStats.mean(edges);
    }

    public static void main(String[] args) {
        
        int T = Integer.parseInt(args[0]);
        
        int edgesQF[] = new int[T];
        int edgesQU[] = new int[T];
        
        double prevQF = timeTrialForQF(T, 125, edgesQF);
        double prevQU = timeTrialForWeiQU(T, 125, edgesQU);
        
        for(int N = 250; true; N += N) {
            
            double timeQF = timeTrialForQF(T, N, edgesQF);
            double timeQU = timeTrialForWeiQU(T, N, edgesQU);
            
            double meanQFConnect = mean(edgesQF);
            double meanQUconnect = mean(edgesQU);
            
            StdOut.printf("%6d %7.1f %7.1f %7.1f %7.1f\n", N, meanQFConnect, timeQF/prevQF, meanQUconnect, timeQU/prevQU);
            
            prevQF = timeQF;
            prevQU = 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 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 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   761.1     2.9   761.4     1.0
   500  1698.6     2.8  1717.8     5.2
  1000  3739.0     3.8  3737.7     2.0
  2000  8184.8     3.7  8174.3     2.1
  4000 17773.4     3.9 17799.1     2.2
  8000 38312.6     4.1 38229.6     2.2

算法(Algorithms)第4版 练习 1.5.22