1.cpp

#include <map>
#include <stdio.h>
#include <unordered_map>
#include <vector>
using namespace std;
vector<int> twoSum(vector<int> &numbers, int target)
{
    //Key is the number and value is its index in the vector.
    unordered_map<int, int> hash;
    vector<int> result;
    for (int i = 0; i < numbers.size(); i++)
    {
        int numberToFind = target - numbers[i];

        //if numberToFind is found in map, return them
        if (hash.find(numberToFind) != hash.end())
        {
            //+1 because indices are NOT zero based
            result.push_back(hash[numberToFind] + 1);
            result.push_back(i + 1);
            return result;
        }

        //number was not found. Put it in the map.
        hash[numbers[i]] = i;
    }
    return result;
}