快排

public:
    void QiuckSort(vector<int>& input, int l, int r){
        if(l >= r) return;
        int x = input[l], i = l - 1, j = r + 1;
        while(i < j){
            do i++; while(input[i] < x);
            do j--; while(input[j] > x);
            if(i < j) swap(input[i], input[j]);
        }
        QiuckSort(input, l, j);
        QiuckSort(input, j + 1, r);
    }
    vector<int> GetLeastNumbers_Solution(vector<int> input, int k) {
        vector<int> ret;
        QiuckSort(input, 0, input.size()-1);
        for(int i = 0; i < k; ++i){
            ret.push_back(input[i]);
        }
        return ret;
    }
};

要时刻记得容器vector的函数