最小的k个数

输入n个整数，找出其中最小的K个数。例如输入4,5,1,6,2,7,3,8这8个数字，则最小的4个数字是1,2,3,4,。

解法1： 最大堆

vector<int> GetLeastNumbers_Solution(vector<int> input, int k) {
        vector<int> rr;
        if(input.empty()||k > input.size()|| k<=0)
            return rr;
        for(int i = 0; i < k; i++)
        {
            rr.push_back(input[i]);
        }
        make_heap(rr.begin(),rr.end());
        for(int i = k; i < input.size();i++)
        {
            if(input[i]<rr[0])
            {
                pop_heap(rr.begin(),rr.end());
                rr.pop_back();
                rr.push_back(input[i]);
                push_heap(rr.begin(),rr.end());
            }
        }
        return rr;
   }

解法2：multiset

vector<int> GetLeastNumbers_Solution(vector<int> input, int k) {
        vector<int> rr;
        if(input.empty()||k > input.size()|| k<=0)
            return rr;
        multiset<int, greater<int>> leastNumbers;
        multiset<int, greater<int> >::iterator iterGreater;
        
        for(int i = 0; i < input.size(); i++)
        {
            if(leastNumbers.size() < k)
                leastNumbers.insert(input[i]);
            else
            {
               iterGreater = leastNumbers.begin();
                if(input[i] < *iterGreater)
                {
                    leastNumbers.erase(*iterGreater);
                    leastNumbers.insert(input[i]);
                }
               
            }
        }
        for(auto ii = leastNumbers.begin(); ii!=leastNumbers.end();ii++)
        rr.push_back(*ii);
    
        return rr;
        
        
        
    }