【数据结构与算法面试题】查找最小的k个数

int swap(int *a, int start, int end, int point_index){
    int par_point = a[point_index];
    while (start < end){
        if (a[start] >= par_point && a[end] <= par_point){
            int tmp = a[start];
            a[start] = a[end];
            a[end] = tmp;
            start ++;
            end --;
        }else if(a[start] < par_point){
            start ++;
        }else{
            end --;
        }
    }
    return start;
}

void get_min_k(int *a, int length, int k){
    if (k > length || NULL == a || length <= 0) return;

    int new_index = swap(a, 0, length-1, k);
    while (true){
        if (new_index == k) break;
        else if (new_index > k){
            new_index = swap(a, 0, new_index, k);
        }else{
            new_index = swap(a, new_index, length-1, k);
        }
    }
}

void get_min_k(int *a, int length, int k, set<int> &s){
    if (k > length || NULL == a || length <= 0) return;

    for (int i = 0; i < length; i++){
        if (s.size() < k){
            s.insert(a[i]);
        }else{
            set<int>::iterator it = --s.end();
            if (a[i] < *it){
                s.erase(*it);
                s.insert(a[i]);
            }
        }
    }
}