1 public class PercolationStats { 2  3     private int N; 4     private int T; 5     private double[] results; 6  7     public PercolationStats(int N, int T) { 8         if (N <= 0 || T <= 0) { 9             throw new java.lang.IllegalArgumentException(10                     "N or T must be greater than 0");11         }12 13         this.N = N;14         this.T = T;15         results = new double[T];16 17         for (int t = 0; t < T; t++) {18             results[t] = run();19         }20     }21 22     private double run() {23         Percolation percolation = new Percolation(N);24         double count = 0;25 26         while (!percolation.percolates()) {27             count++;28 29             // pick a random site30             // (N+1 because second value to uniform is exclusive)31             int i = StdRandom.uniform(1, N + 1);32             int j = StdRandom.uniform(1, N + 1);33 34             // generate new random sites until a blocked one is found35             while (percolation.isOpen(i, j)) {36 37                 i = StdRandom.uniform(1, N + 1);38                 j = StdRandom.uniform(1, N + 1);39 40             }41 42             // open that site43             percolation.open(i, j);44 45         }46         return count / (N * N); // percolation threshold estimate47     }48 49     public double mean() {50         return StdStats.mean(results);51     }52 53     public double stddev() {54         return StdStats.stddev(results);55     }56 57     public double confidenceHi() {58         return mean() - 1.96 * stddev() / Math.sqrt(T);59     }60 61     public double confidenceLo() {62         return mean() + 1.96 * stddev() / Math.sqrt(T);63     }64 65     public static void main(String[] args) {66 67         int N;68         int T;69 70         if (args.length == 0) {71             N = 100;72             T = 10;73         } else {74             N = Integer.parseInt(args[0]);75             T = Integer.parseInt(args[1]);76         }77 78         // double startTime = System.nanoTime();79         PercolationStats stats = new PercolationStats(N, T);80 81         double confidenceLow = stats.confidenceHi();82         double confidenceHigh = stats.confidenceLo();83 84         System.out.println("mean                    = " + stats.mean());85         System.out.println("stddev                  = " + stats.stddev());86         System.out.println("95% confidence interval = " + confidenceLow + ", "87                 + confidenceHigh);88 89         // performance measuring90         // double endTime = System.nanoTime();91         // System.out.println("time cost: " + (endTime - startTime));92 93     }94 }