class Solution {
public:
    int bsearch(vector<int>& nums, int target) {
        int left = 0;
        int right = nums.size() - 1;

        while(left <= right){
            int mid = (right - left)/2 + left;
            if(nums[mid] < target){
                left = mid + 1;
            } else if(nums[mid] > target){
                right = mid - 1;
            } else if(nums[mid] == target){
                return mid;
            }
        } 

        return -1;
    }
};

class Solution {
public:
    int left_bound(vector<int>& nums, int target) {
        int left = 0, right = nums.size() - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] > target) {
                right = mid - 1;
            } else if (nums[mid] == target) {
                // 别返回，锁定左侧边界
                right = mid - 1;
            }
        }
        // 最后要检查 left 越界的情况
        if (left >= nums.size() || nums[left] != target) {
            return -1;
        }
        return left;
};

class Solution {
public:
    int right_bound(vector<int>& nums, int target) {
        int left = 0, right = nums.size() - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] > target) {
                right = mid - 1;
            } else if (nums[mid] == target) {
                // 别返回，锁定右侧边界
                left = mid + 1;
            }
        }
        // 最后要检查 right 越界的情况
        if (right < 0 || nums[right] != target) {
            return -1;
        }
        return right;
    }
};