二分

class Solution {
public:
    int getNumberOfK(vector<int>& nums , int k) {
        if(nums.size() == 0)
            return 0;
        int l = 0, r = nums.size()-1;
        while(l < r)
        {
            int mid = l + r >> 1;
            if(nums[mid] >= k)
                r = mid;
            else
                l = mid + 1;
        }
        int res = 0;
        while(nums[r] == k)
        {
            res++;
            r++;
        }
        return res;
    }
};