1. public static int rank(int key, int[] a)    //a为一个升序数组
    2.     {
    3.         int lo = 0;
    4.         int hi = a.length - 1;
    5.         while (lo <= hi)
    6.         {
    7.             int mid = lo + (hi - lo) / 2;
    8.             if (key < a[mid])
    9.                 hi = mid - 1;
    10.             else if (key > a[mid])
    11.                 lo = mid + 1;
    12.             else
    13.                 return mid;
    14.         }
    15.         return -1;
    16.     }