两个二分板子

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

        return l;
    }

    int findLast(vector<int>& nums, int x){
        int l = 0, r = nums.size()-1;
        while(l < r){
            int mid = l+r+1>>1;
            if(nums[mid] <= x)l = mid;
            else r = mid-1;
        }

        return l;
    }
};