2.二分查找

public static int binarySearchLeft(int[] nums, int left, int right, int key){
    while (left < right){
        int mid = (left + right ) / 2;
        if (nums[mid] >= key){ 
            right = mid;
        }
        else{
            left = mid + 1;
        }
    }
    return left;
}

public static  int binarySearchRight(int[] nums, int left, int right, int key){
    while (left < right){
        int mid = (left + right + 1) / 2; //修正
        if (nums[mid] <= key){
            left = mid;
        }
        else{
            right = mid - 1;
        }
    }
    return left;
}