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

std::pair<int, int> twoSum(const std::vector<int>& nums, int target) {
    std::unordered_map<int, int> freq; // number → count

    for (int i = 0; i < nums.size(); ++i) {
        freq[nums[i]]++;
    }

    for (int i = 0; i < nums.size(); ++i) {
        int complement = target - nums[i];

        // Case 1: nums[i] != complement
        if (complement != nums[i] && freq[complement] > 0) {
            return {nums[i], complement};
        }

        // Case 2: nums[i] == complement, need at least 2 occurrences
        if (complement == nums[i] && freq[nums[i]] > 1) {
            return {nums[i], nums[i]};
        }
    }

    return {-1, -1}; // Not found
}

int main() {
    std::vector<int> nums = {12, 12, 13};
    int target = 24;

    auto result = twoSum(nums, target);

    if (result.first != -1) {
        std::cout << "Found: " << result.first << " + " << result.second << " = " << target << "\n";
    } else {
        std::cout << "No valid pair found.\n";
    }

    return 0;
}