# Two Sum LeetCode Solution

·1 min
Leetcode

Given an array of integers `nums` and an integer `target`, return indices of the two numbers such that they add up to `target`.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

Example 1:

Input: nums = [2,7,11,15], target = 9 Output: [0,1] Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6 Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6 Output: [0,1]

Constraints:

• `2 <= nums.length <= 103`
• `-109 <= nums[i] <= 109`
• `-109 <= target <= 109`
• Only one valid answer exists.

## Solution #

class Solution { public: vector twoSum(vector& a, int target) { unordered_map<int, int> m; // element and its index mapping vector res;

``````    m\[a\[0\]\] = 0; // first index

for(int i=1; i<a.size(); i++) {
int diff = target - a\[i\];

if(m.find(diff) != m.end()) {
res.push\_back(m\[diff\]);
res.push\_back(i);
}

m\[a\[i\]\] = i;
}

return res;
}
``````

};