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# 136. Single Number

## Easy

***

Given a **non-empty** array of integers `nums`, every element appears *twice* except for one. Find that single one.

You must implement a solution with a linear runtime complexity and use only constant extra space.

 

**Example 1:**

```
Input: nums = [2,2,1]
Output: 1
```

**Example 2:**

```
Input: nums = [4,1,2,1,2]
Output: 4
```

**Example 3:**

```
Input: nums = [1]
Output: 1
```

 

**Constraints:**

* `1 <= nums.length <= 3 * 104`
* `-3 * 104 <= nums[i] <= 3 * 104`
* Each element in the array appears twice except for one element which appears only once.