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

std::pair<int, int> twoSum(const std::vector<int>& nums, int target) {
    std::unordered_map<int, int> seen; // key = number, value = index

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

        if (seen.find(complement) != seen.end()) {
            return {seen[complement], i}; // return indices of the two numbers
        }

        seen[nums[i]] = i;
    }

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

int main() {
    std::vector<int> nums = {8, 3, 5, 7, 1};
    int target = 10;

    std::pair<int, int> result = twoSum(nums, target);

    if (result.first != -1) {
        std::cout << "Indices: " << result.first << ", " << result.second << "\n";
        std::cout << "Numbers: " << nums[result.first] << " + " << nums[result.second] << " = " << target << "\n";
    } else {
        std::cout << "No pair found.\n";
    }

    return 0;
}