[Algorithms(Princeton)] Week1

 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 site
30             // (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 found
35             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 site
43             percolation.open(i, j);
44 
45         }
46         return count / (N * N); // percolation threshold estimate
47     }
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 measuring
90         // double endTime = System.nanoTime();
91         // System.out.println("time cost: " + (endTime - startTime));
92 
93     }
94 }