---
# System prepended metadata

title: '#136 Single Number'
tags: [LeetCode, ' Top100']

---

---
title: "#136 Single Number"
tags: LeetCode, Top100
---
#136. Single Number

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

**Follow up**: Could you implement a solution with a linear runtime complexity and without using extra memory?

Example 1:
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>Input: nums = [4,1,2,1,2]
Output: 4

解題思維
--
裡用只會有獨立一個，且重複一次的特性。將Input變成集合再\*2，減掉Input。


Math
--
```python=
class Solution:
    def singleNumber(self, nums: List[int]) -> int:

        return 2 * sum(set(nums)) - sum(nums)

```