# 0001. Two Sum

<https://leetcode.com/problems/two-sum>

## Description

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*****&#x20;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 <= 104`
* `-109 <= nums[i] <= 109`
* `-109 <= target <= 109`
* **Only one valid answer exists.**

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

## ac

```java
test
```