Comment by dzorz

Here is a solution in C++. It reads K and then N numbers from stdin and then prints K largest.

The complexity of nth_element is O(N).

    #include <algorithm>
    #include <vector>
    #include <iostream>
    #include <iterator>

    using namespace std;

    int main() {
        int K;
        cin >> K;
        vector<int> numbers((istream_iterator<int>(cin)),
                            istream_iterator<int>());
        nth_element(numbers.begin(), numbers.begin() + K, numbers.end(),
                    greater<int>());
        for (int i = 0; i < K; ++i) {
            cout << numbers[i] << ' ';
        }
        cout << '\n';
    }

Input:

    5
    1 9 1 3 7 8 2 11 2 5 5 9 1 7

Output:

    7 9 9 11 8

Note: the output is not sorted.