题解 | #数字在升序数组中出现的次数#

class Solution {
public:

    int find(vector<int> res, float a){
        int head = 0 , tail = res.size() - 1;
        int mid = ( tail + head ) / 2;
        while(tail >= head){
            if(res[mid] > a) tail = mid - 1;
            if(res[mid] < a) head = mid + 1;
            mid = ( tail + head ) / 2;
        }
        return tail;  //这里返回头或者尾都行，不要分情况讨论，否则有些情况会差1
    }

    int GetNumberOfK(vector<int> data ,int k) {
        return find(data,k+0.5) - find(data,k-0.5);
    }
};