AlgorithmsI Programming Assignment 1: PercolationStats.java

import edu.princeton.cs.algs4.StdOut;
import edu.princeton.cs.algs4.StdRandom;
import edu.princeton.cs.algs4.StdStats;
/*
*How do I generate a site uniformly at random among all blocked sites for use in PercolationStats?
* Pick a site at random (by using StdRandom to generate two integers between 1 and N)
* and use this site if it is blocked; if not, repeat.
*/
public class PercolationStats {
private int T; //T independent experiments
private double[] fraction;

public PercolationStats(int N, int T) {  // perform T independent experiments on an N-by-N grid
if (N <= 0 || T <= 0) {
throw new IllegalArgumentException("N and T must be bigger than 0");
}
this.T = T;
fraction = new double[T];

for (int count = 0; count < T; count++) {
Percolation pr =  new Percolation(N);
int openedSites = 0;
while (!pr.percolates()) {
int i = StdRandom.uniform(1, N+1);
int j = StdRandom.uniform(1, N+1);
if (!pr.isOpen(i, j)) {
pr.open(i, j);
openedSites++;
}
}
fraction[count] = (double) openedSites / (N * N);
}
}

public double mean() {                     // sample mean of percolation threshold
return StdStats.mean(fraction);
}

public double stddev() {                 // sample standard deviation of percolation threshold
return StdStats.stddev(fraction);
}

public double confidenceLo() {           // low  endpoint of 95% confidence interval
return mean() - 1.96 * stddev() / Math.sqrt(T);
}

public double confidenceHi() {      // high endpoint of 95% confidence interval
return mean() + 1.96 * stddev() / Math.sqrt(T);
}

public static void main(String[] args)    // test client (described below)
{
int N = Integer.parseInt(args[0]);
int T = Integer.parseInt(args[1]);
PercolationStats ps = new PercolationStats(N, T);
StdOut.println("mean                    = " + ps.mean());
StdOut.println("stddev                  = " + ps.stddev());
StdOut.println("95% confidence interval = "+ps.confidenceLo()+", "+ ps.confidenceHi());
}
}