# 136. Single Number Leetcode Solution

## Single Number Leetcode 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.

## Single Number Leetcode Solution :

### Constraints :

• 1 <= nums.length <= 3 * 10^4
• -3 * 10^4 <= nums[i] <= 3 * 10^4
• Each element in the array appears twice except for one element which appears only once.

### Example 1:

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

### Example 2:

• Input: nums = [1]
• Output: 1

Intution :

We can do this using unordered_map as we need to count the frequency of element.

Approach :

• Make an unordered map in which store the count of all values present in an array.
• Traverse through map and check which value has count 1 and then break through loop and store that value in ans variable.
• Return ans.

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