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());

   }

}