int binarySearch(int arr[], int left, int right, int target) {
    while (left <= right) {
        ________________________________ // 在此处填入代码

        if (arr[mid] == target)
            return mid;
        else if (arr[mid] < target)
            left = mid + 1;
        else
            right = mid - 1;
    }
    return -1;
}