[Algorithms(Princeton)] Week1 - PercolationStats

 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));

     }
 }