题解 | #数字在升序数组中出现的次数#

//由于数组有序，所以使用二分查找方法定位k的第一次出现位置和最后一次出现位置
class Solution {
public:
    int GetNumberOfK(vector<int> data ,int k) {
        int lower = getLower(data,k);
        int upper = getUpper(data,k);
        return upper - lower + 1; 
    }

    //获取k第一次出现的下标
    int getLower(vector<int> data,int k){
        int start = 0,end = data.size()-1;
        int mid = (start + end)/2;
        while(start <= end){
            if(data[mid] < k){
                start = mid + 1;
            }else{
                end = mid - 1;
            }
            mid = (start + end)/2;
        }
        return start;
    }
    //获取k最后一次出现的下标
    int getUpper(vector<int> data,int k){
         int start = 0,end = data.size()-1;
        int mid = (start + end)/2;
        while(start <= end){
            if(data[mid] <= k){
                start = mid + 1;
            }else{
                end = mid - 1;
            }
            mid = (start + end)/2;
        }
        return end;
    }
};