获得最小的topK

set、multiset都是集合类，差别在与set中不允许有重复元素，multiset中允许有重复元素。
sets和multiset内部以平衡二叉树实现


#include<iostream>
#include <stdio.h> 
#include <stack>
#include <vector>
#include <set> 

using namespace std;

typedef multiset<int, greater<int> > intSet;
typedef multiset<int, greater<int> >::iterator setIterator;

void get_least_numbers(const vector<int>& data, intSet& least_numbers, int k) {
    least_numbers.clear();
    if (k < 1 || data.size() < k) {
        return;
    }
    vector<int>::const_iterator iter = data.begin();
    for(; iter != data.end(); iter++) {
        if (least_numbers.size() < k) {
            least_numbers.insert(*iter);
        }
        else {
            setIterator iter_greatest = least_numbers.begin();
            if (*iter < *(least_numbers.begin())) {
                least_numbers.erase(iter_greatest);
                least_numbers.insert(*iter);
            }
        }
    }
    
}

int main()
{
    int a[8] = {4, 2, 6, 7, 9, 5, 1, 3};
    int length = sizeof(a) / sizeof(a[0]);

    const vector<int> data(a, a+length);
    multiset<int, greater<int> > least_numbers;
    
    get_least_numbers(data, least_numbers, 3);
    for(setIterator it=least_numbers.begin(); it != least_numbers.end(); it++) {
        cout << *it << " " << endl;
    }
    return 0;
}