# [Leet Code] Single Number

Leet code: https://leetcode.com/problems/single-number/

Problem:

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

Solution:

`class Solution(object):`

def singleNumber(self, nums):

"""

:type nums: List[int]

:rtype: int

"""

answers = []

for i in nums:

if i in answers:

answers.pop(answers.index(i))

else:

answers.append(i)

return answers[0]