关于c++:C-STL中的Binary-search二分查找

左闭右开写法

• 查找某个元素是否呈现。

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

• 查找第一个大于或等于某个元素的地位

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

• 查找第一个大于某个元素的地位。

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