题解 | #数字在升序数组中出现的次数#

class Solution {
public:
    int GetNumberOfK(vector<int> data ,int k) {
        //左边界 和 右边界
       int lbound = 0,rbound = 0;
       int l = 0,r = data.size();
       // 二分法找左边界，要求左边的值小于k，右边的值>=k
        while(l<r){
            int mid = (l+r)/2;
            if(data[mid] < k) l = mid+1;
            else r = mid;
            //找左边界 如果mid小于k说明可以mid+1 mid必不为k
        }
        lbound = l;
        l = 0,r = data.size();
        while(l<r){
            int mid = (l+r)/2;
            if(data[mid]<=k) l = mid+1;
            else r = mid;
        }
        rbound = l;
        return rbound - lbound;
        
    }
};

二分很容易想到 就是具体的界限最好手动算一下