(Easy) Single Number

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

 

풀이

class Solution:

def singleNumber(self, nums: List[int]) -> int:

  dic = {}

 

  for i in nums:

    # dic is None 은 빈값이 왔을때 오류를 뱉는다.

    if dic.get(i) is None:

      dic[i] = 1

    else:

      dic[i] += 1

 

  for i in nums:

    if dic[i] == 1:

return i