求一个数组的第k大数

void findkmax(int* arr,int len,int k){
    if(arr == NULL || len < k || len <= 0 ){
        return;
    }
    multiset<int> set;


    for (int j = 0; j < len; ++j) {
        if(set.size() < k){
            set.insert(arr[j]);
        } else{
            multiset<int,greater<int>>::iterator it = set.begin();
            int first = *it;
            if(first < arr[j]){
                set.erase(it);
                set.insert(arr[j]);
            }
        }
    }

    for (multiset<int,greater<int>>::iterator it = set.begin(); it != set.end() ; ++it) {
        cout<<*it<<" ";
    }

    cout<<endl;


}