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# Two Sum

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:**

<pre><code><strong>Input: nums = [2,7,11,15], target = 9
</strong><strong>Output: [0,1]
</strong><strong>Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
</strong></code></pre>

**Example 2:**

<pre><code><strong>Input: nums = [3,2,4], target = 6
</strong><strong>Output: [1,2]
</strong></code></pre>

**Example 3:**

<pre><code><strong>Input: nums = [3,3], target = 6
</strong><strong>Output: [0,1]
</strong></code></pre>

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**Constraints:**

* `2 <= nums.length <= 104`
* `-109 <= nums[i] <= 109`
* `-109 <= target <= 109`
* **Only one valid answer exists.**

&#x20;

**Follow-up:** Can you come up with an algorithm that is less than `O(n2)` time complexity?

```go
package main

func twoSum(nums []int, target int) []int {
	seen := make(map[int]int)
	for i, v := range nums {
		if j, ok := seen[target-v]; ok {
			return []int{i, j}
		}
		seen[v] = i
	}
	return *new([]int)
}
```