//有序数组二分查找
int bsearch(int array[], int left, int right, int target)
{
    while (left <= right)
    {
        int mid = (left+right)/2;
        if (array[mid] == target) return mid;
        else if (array[mid] > target) right=mid-1;
        else left=mid +1;
    }
    return -1;
}