二分查找（Binary Search）

 1 int BinarySearch(int *array, int N, int key)
 2 {
 3     int NotFound = -1;
 4     int left, right, mid;
 5     left  = 0;
 6     right = N - 1;
 7 
 8     while(left <= right)
 9     {
10         mid = (left + right) / 2;
11 
12         if (key < array[mid])
13             right = mid - 1;
14         else if (key > array[mid])
15             left  = mid + 1;
16         else
17             return mid;
18     }
19 
20     return NotFound;
21 }