编程之美：二分查找

前三个问题不讲，已经解决过了

现在写最后两个

1.最大的i使得arr[i]小于v，其实就是求等于v的下界的前一个元素。
2.最小的i使得arr[i]大于v，其实就是求等于v的上界的后一个元素。

#include <iostream>
#include<vector>
using namespace std;

int indexOfMaxLess(vector<int>& nums, int target){
    int len = nums.size();
    if (len == 0)
        return -1;
    int left = 0, right = len - 1;
    while (left <= right){
        int mid = left + (right - left) / 2;
        if (target <= nums[mid])
            right = mid - 1;
        else
            left = mid + 1;
    }

    if (left > 0){
        return left - 1;
    }

    return -1;
}

int indexOfMinBigger(vector<int>& nums, int target){
    int len = nums.size();
    if (len == 0)
        return -1;
    int left = 0, right = len - 1;
    while (left <= right){
        int mid = left + (right - left) / 2;
        if (target >= nums[mid])
            left = mid + 1;
        else
            right = mid - 1;
    }
    if (right < len - 1){
        return right + 1;
    }
    return -1;
}


int main()
{

    vector<int> nums = { 0, 0, 2,2, 3, 3 };
    cout << indexOfMaxLess(nums, 2) << endl;
    cout << indexOfMinBigger(nums, 2) << endl;

    cout << "-------------------" << endl;

    cout << indexOfMaxLess(nums, 0) << endl;
    cout << indexOfMinBigger(nums, 0) << endl;

    cout << "-------------------" << endl;

    cout << indexOfMaxLess(nums, 3) << endl;
    cout << indexOfMinBigger(nums, 3) << endl;

    return 0;
}

结果：

1
4
-------------------
-1
2
-------------------
3
-1