item30，最小的k个数

typedef std::multiset<int,greater<int> > intset;
    typedef std::multiset<int,greater<int> >::iterator iteratorset;

    void getLeastNumber(vector<int> nums,intset& leastNumber,int k){
        int length = nums.size();

        leastNumber.clear();
        if(length <k) return;
        for(auto i:nums){
            if(leastNumber.size()<(unsigned int)k){
                leastNumber.insert(i);
            }else{
                iteratorset itset = leastNumber.begin();
                if(i<*itset){
                    leastNumber.insert(i);
                    leastNumber.erase(leastNumber.begin());
                }
            }///if-else
        }///for
    }///end-function