二分查找的简单示例

一个整数键和一个有序整数数组，返回键值在数组中的索引

    int rank(int key, int[] a) {
        int low = 0;
        int high = a.length - 1;
        while (low <= high) {
            int mid = low + (high - low) / 2;
            if (key < a[mid]) {
                high = mid - 1;
            } else if (key > a[mid]) {
                low = mid + 1;
            } else {
                return mid;
            }
        }
        return -1;
    }