1

认识到上下界

2

copy version

class Solution {
public:
    int GetNumberOfK(vector<int> nums ,int target) {
        int lbound = 0, rbound = 0;
        // 寻找xia界
        int l = 0, r = nums.size();
        while (l < r) {
            int mid = l + (r - l) / 2;
            if (nums[mid] < target) {
                l = mid + 1;
            }
            else {
                r = mid;
            }
        }
        lbound = l;
        
        // 寻找shang界
        l = 0, r = nums.size();
        while (l < r) {
            int mid = l + (r - l) / 2;
            if (nums[mid] <= target) {
                l = mid + 1;
            }
            else {
                r = mid;
            }
        }
        rbound = r;
        return rbound - lbound;
    }
};