Problem

Given a set of integers, write a function that returns true if there exists a pair of integers in the set that sum up to a given target value. Return false otherwise.
Example input: [3, 5, 2, -4, 8, 11], target = 7
Example output: true (5 + 2 = 7)

Solution

#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;

bool sum_exists(vector<int>& v, int target) {
    unordered_map<int, int> m;
    for (int i = 0; i < v.size(); i++) {
        if (m.find(v[i]) != m.end()) {
            return true;
        }
        m[target - v[i]] = v[i];
    }
    return false;
}

int main() {
    vector<int> v = {3, 5, 2, -4, 8, 11};
    int target = 7;
    cout << sum_exists(v, target) << endl;
    return 0;
}