LeetCode: TwoSum Solution - c++

Question

I'm trying to use a map in order to make the algorithm for this answer https://leetcode.com/problems/two-sum/#/description O(n), but for some reason i'm getting the improper indices for a lot of test cases i'm trying
From what I can tell, I'm doing the checks properly for the iterators, however these are kind of new to me, and i'm not entirely sure if i'm returning the correct indices that I want.
//My Code:
#include <iostream>
#include <cstdio>
#include <array>
#include <vector>
#include <map>
std::vector<int> twoSum(int nums[], int size, int target)
{
std::vector<int> answer;
std::map<int, int> myMap;
std::map<int, int>::iterator it;
std::cout << size << std::endl;
for (int i = 0; i < size; i++)
{
myMap.insert(std::pair<int, int>(nums[i], i));
int indexItOne = distance(myMap.begin(), myMap.find(nums[i]));
int indexItTwo = distance(myMap.begin(), myMap.find(target-nums[i]));
it = myMap.find(target - nums[i]);
if (it != myMap.begin() || indexItOne != indexItTwo)
{
answer.push_back(i);
answer.push_back(distance(myMap.begin(), myMap.find(target - nums[i])));
return answer;
}
}//for
}//twoSum

Answer 1

You are correct in that the map should be a mapping from num to the index of that num, but it should not be inserted into the map right away. This is due to the constraint of the problem that
you may not use the same element twice.
Therefore, the algorithm would go something more like this:
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
// Create a mapping from num -> index of num
unordered_map<int, int> m;
for(int i = 0; i < nums.size(); i++) {
// Check if we have seen our buddy
int buddy = target - nums[i];
auto buddyIt = m.find(buddy);
if(buddyIt != m.end()) {
// Buddy found, return answer
return vector<int>{ buddyIt->second, i };
}
// Buddy not found, insert current num into buddy map
m[nums[i]] = i;
}
}
};