class Solution {
public:
    int getNumberOfK(vector<int>& nums , int k) {
        if(nums.empty()) return 0;
        int n=nums.size();
        int res=0; 
        //--------------------------------------------- 寻找第一次出现的位置
        int l=0,r=n-1;
        while(l<r){
             int mid =l+r>>1;
            if(nums[mid]<k)  l=mid+1;
            else r = mid;
        }
        if(nums[l]!=k) return 0;  
        int a =l;
       // -------------------------------------------- 寻找最后一次出现的位置        
          l=0,r=n-1;
        while(l<r){
            int mid =l+r+1>>1;
            if(nums[mid]<=k)  l=mid;
            else r = mid-1;
        }
        int b = l;
        //------------------------------------------------
        res=b-a+1;
        return res;

    }
};