PercolationStats.java

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

public class PercolationStats {
    private double[] fractions;

    // perform independent trials on an n-by-n grid
    public PercolationStats(int n, int trials) {
        if (n <= 0 || trials <= 0) {
            throw new IllegalArgumentException("Invalid argument!");
        }

        int count = trials;
        fractions = new double[trials];

        while (count > 0) {
            int x = 0;

            Percolation percolation = new Percolation(n);

            while (!percolation.percolates()) {
                int row = StdRandom.uniformInt(1, n + 1);
                int col = StdRandom.uniformInt(1, n + 1);

                if (!percolation.isOpen(row, col)) {
                    percolation.open(row, col);
                    x++;
                }
            }
            fractions[trials-count] = (double) x / (n * n);
            count--;
        }
    }

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

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

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

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

    // test client (see below)
    public static void main(String[] args) {
        int n = Integer.parseInt(args[0]);
        int trials = Integer.parseInt(args[1]);

        PercolationStats percolationStats = new PercolationStats(n, trials);

        double mean = percolationStats.mean();

        StdOut.println("mean                   " + " = " + mean);
        StdOut.println("stddev                 " + " = " + percolationStats.stddev());
        StdOut.println("95% confidence interval" + " = " + "[" + percolationStats.confidenceLo() + ", " + percolationStats.confidenceHi() + "]");
    }
}