Solving the Single Number problem in Python

The challenge

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

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Example 1:

Input: [2,2,1]
Output: 1

Example 2:

Input: [4,1,2,1,2]
Output: 4

The solution in Python

def singleNumber(nums): # create a dictionary/hashmap found = {} # loop through the nums for i in nums: # add to map if not found if i not in found: found[i] = i else: # otherwise remove it del found[i] # loop through the found map and return the first item for i in found: return i
Code language: Python (python)
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