题解 | #c++ 给出三种方法，哈希表、二分查找、库函数#

class Solution {
public:
    int GetNumberOfK(vector<int> data ,int k) {
        return origMethod(data, k);
    }
    /*方法一： 哈希表*/
    int hashMethod(vector<int> data,int k){
        unordered_map<int,int> result;
        for(int val:data){
            if(val == k){
                ++result[val];
            }
        }
        return result[k];
    }
    /*方法二： 二分查找*/
    /*找最左边索引*/
    int bisserch(vector<int>data, int k,int left,int right){
        if(left > right || data[left] > k || data[right] < k){
            return -1;
        }else{
            int mid = (left+right)/2;
            if(data[left] == k){
                return left;
            } int dp = bisserch(data,k, left, mid);
            if(dp != -1){
                return dp;
            }
            return bisserch(data,  k, mid+1, right);
        }
    }/*找最右边索引*/
    int bisserch1(vector<int> data,int k,int left,int right){
        if(left > right || data[left] > k|| data[right] <k){
            return -5;
        }else{
            int mid = (left+right)/2;
            if(data[right] == k){
                return right;
            }int dpi = bisserch1(data, k,  mid+1, right);
            if(dpi != -5){
                return dpi;
            }return bisserch1(data, k,  left, mid);
        }
    }
    /*方法3 ：库函数 */
    int origMethod(vector<int> data,int k){
        auto result = equal_range(data.begin(),data.end(),k);
        //second 左界，frist右界
       
        return result.second - result.first;
    }
};