## Challenge Statement

- Given an array of integers,
*nums,*and an integer target,*target*, return*indices of the two numbers such that they add up to target*. - You may assume that each input would have
, and you may not use the*exactly*one solution*same*element twice. - You can return the answer in any order.
- This challenge corresponds to LeetCode #1.

### Constraints

`2 <= len(nums) <= 10`

^{4}`-10`

^{9}<= nums[i] <= 10^{9}`-10`

^{9}<= target <= 10^{9}**Only one valid answer exists.**

**Example 1:**

**Input:**` nums = [2, 7, 11, 15]`

, `target = 9`

**Output:** `[0, 1]`

**Explanation:** 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]`

## Solution

Below is my solution and some test cases. This solution has a **linear time complexity O(n)** and a **linear space complexity O(n)**, where *n* is the length of the input list *nums*.