Finding three elements that sum to K

Question

I wrote the following to find two elements that sum to K

#include 
#include 

void sum_equal_to_k(int *a, int n, int k) { /*         


        

Answer 1

The problem is known as 3SUM. There's an O(n^2) algorithm for solving it that you can find here, that doesn't require any hashing.

It'll be simpler if you just use vector (you're already using unordered_map anyway, right?):

void sum3_k(std::vector<int> s, int k) {
    std::sort(s.begin(), s.end());

    for (size_t i = 0; i < s.size() - 2; ++i) {
        size_t start = i + 1;
        size_t end = s.size() - 1;

        while (start < end) {
            int sum = s[i] + s[start] + s[end];
            if (sum == k) {
                std::cout << s[i] << " " << s[start] << " " << s[end] << std::endl;
                ++start, --end;
            }
            else if (sum > k) {
                --end;
            }
            else {
                ++start;
            }
        }
    }
}