二分查找 Binary Search

 1 int
 2 BinarySearch(int arr[], int key, int left, int right)
 3 {
 4     if (left > right) { 
 5         return -1; 
 6     }
 7     
 8     int middle = (left + right) / 2;
 9     
10     if (arr[middle] == key) {
11         return middle;
12     } else if (arr[middle] > key) {
13         BinarySearch(arr, key, left, middle-1);
14     } else if (arr[middle] < key) {
15         BinarySearch(arr, key, middle+1, right);
16     }
17 }