2017年11月20日。

  1 import java.util.Arrays;
  2 
  3 public class Program
  4 {
  5     public static void main(String[] args)
  6     {
  7 //        testBinarySearch(‘+‘);
  8         euclid(104, 24);
  9     }
 10 
 11     public static int gcd(int p, int q)
 12     {
 13         System.out.println("p: " + p + ", q: " + q);
 
 14         if (q == 0) return p;
 15         int r = p % q;
 16         return gcd(q, r);
 17     }
 18 
 19     public static int lg(double n)
 20     {
 21         double m = Math.log(n) / Math.log(2.0);
 22         return (int) Math.floor(m);
 23     }
 24 
 25     public static int[] histogram(int[] a, int
 
 m)
 26     {
 27         int[] M = new int[m];
 28         for (int i = 0; i < a.length; i++) {
 29             if (i == a[i])
 30                 M[i] += 1;
 31         }
 32         return M;
 33     }
 34 
 35     public static int mystery(int a, int b)
 36     {
 37         if (b == 0) return 0;
 
 38         if (b % 2 == 0) return mystery(a + a, b / 2);
 39         return mystery(a + a, b / 2) + a;
 40     }
 41 
 42     public static long fibonacci(int n)
 43     {
 44         if (n == 0) return 0;
 45         if (n == 1) return 1;
 46         else return fibonacci(n - 2) + fibonacci(n - 1);
 47     }
 48 
 49     public static long fib(int n)
 50     {
 51         long f1 = 0;
 52         long f2 = 1;
 53         long tm = 0;
 54         while (n > 0) {
 55             tm = f1;
 56             f1 = f1 + f2;
 57             f2 = tm;
 58             n--;
 59         }
 60         return f1;
 61     }
 62 
 63     public static double ln(int n)
 64     {
 65         if (n == 1)
 66             return Math.log10(1);
 67         else
 68             return Math.log10(n) + ln(n - 1);
 69     }
 70 
 71     public static int binarySearch(int key, int[] arr, int lo, int hi, int n)
 72     {
 73         System.out.println("deep: " + n++);
 74         if (lo > hi) return -1;
 75         int mid = lo + (hi - lo) / 2;
 76         if (key < arr[mid])
 77             return binarySearch(key, arr, lo, mid - 1, n);
 78         else if (key > arr[mid])
 79             return binarySearch(key, arr, mid + 1, hi, n);
 80         else
 81             return mid;
 82     }
 83 
 84     public static int binarySearch(int key, int[] arr)
 85     {
 86         return binarySearch(key, arr, 0, arr.length, 0);
 87     }
 88 
 89     public static void testBinarySearch(char ch)
 90     {
 91         int[] arr = {11, 13, 15, 7, 9, 1, 3, 5, 17, 19, 21};
 92         Arrays.sort(arr);
 93         for (int i = 0; i < arr.length; i++) {
 94             System.out.print(arr[i] + (i < arr.length - 1 ? " " : "\n"));
 95         }
 96         int key = 18;
 97         System.out.println(binarySearch(key, arr));
 98     }
 99 
100     public static void euclid(int p, int q)
101     {
102         int r = gcd(p, q);
103         System.out.println(r);
104     }
105 }

練習代碼——《算法（第四版）》（一）