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;
}

}

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