[Algorithms(Princeton)] Week1

public class PercolationStats {

    private int N;
    private int T;
    private double[] results;

    public PercolationStats(int N, int T) {
        if (N <= 0 || T <= 0) {
            throw new java.lang.IllegalArgumentException(
                    "N or T must be greater than 0");
        }

        this.N = N;
        this.T = T;
        results = new double[T];

        for (int t = 0; t < T; t++) {
            results[t] = run();
        }
    }

    private double run() {
        Percolation percolation = new Percolation(N);
        double count = 0;

        while (!percolation.percolates()) {
            count++;

            // pick a random site
            // (N+1 because second value to uniform is exclusive)
            int i = StdRandom.uniform(1, N + 1);
            int j = StdRandom.uniform(1, N + 1);

            // generate new random sites until a blocked one is found
            while (percolation.isOpen(i, j)) {

                i = StdRandom.uniform(1, N + 1);
                j = StdRandom.uniform(1, N + 1);

            }

            // open that site
            percolation.open(i, j);

        }
        return count / (N * N); // percolation threshold estimate
    }

    public double mean() {
        return StdStats.mean(results);
    }

    public double stddev() {
        return StdStats.stddev(results);
    }

    public double confidenceHi() {
        return mean() - 1.96 * stddev() / Math.sqrt(T);
    }

    public double confidenceLo() {
        return mean() + 1.96 * stddev() / Math.sqrt(T);
    }

    public static void main(String[] args) {

        int N;
        int T;

        if (args.length == 0) {
            N = 100;
            T = 10;
        } else {
            N = Integer.parseInt(args[0]);
            T = Integer.parseInt(args[1]);
        }

        // double startTime = System.nanoTime();
        PercolationStats stats = new PercolationStats(N, T);

        double confidenceLow = stats.confidenceHi();
        double confidenceHigh = stats.confidenceLo();

        System.out.println("mean                    = " + stats.mean());
        System.out.println("stddev                  = " + stats.stddev());
        System.out.println("95% confidence interval = " + confidenceLow + ", "
                + confidenceHigh);

        // performance measuring
        // double endTime = System.nanoTime();
        // System.out.println("time cost: " + (endTime - startTime));

    }
}