剑指offer----数字在排序数组中出现的次数

统计一个数字在排序数组中出现的次数。

class Solution {
//数组有序----->  借助二分查找法
//找到第一个key 与 最后一个key
//利用两者下标的差+1 即求得key出现的次数
public:
    int GetNumberOfK(vector data ,int k) {
        int len = data.size();
        if(len < 1)
            return 0;
        int first = GetFirstOfK(data,k);
        int last = GetLastOfK(data,k);
        return last - first + 1;
    }
    int GetFirstOfK(vector data ,int k){
        int len = data.size();
        int start = 0;
        int end = len - 1;
        int mid = (end + start)/2;
        while(start <= end){
            if(data[mid] < k){
                start = mid + 1;
            }
            else
                end = mid - 1;
            mid = (end + start)/2;
        }
        return start;
    }
    
    int GetLastOfK(vector data ,int k){
        int len = data.size();
        int start = 0;
        int end = len - 1;
        int mid = (end + start)/2;
        while(start <= end){
            if(data[mid] <= k){
                start = mid + 1;
            }
            else
                end = mid - 1;
            mid = (end + start)/2;
        }
        return end;
    }
};