Single Number

Problem

https://leetcode.com/problems/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

Constraints:

• 1 <= nums.length <= 3 * 10⁴

• -3 * 10⁴<= nums[i] <= 3 * 10⁴

• Each element in the array appears twice except for one element which appears only once.

Pattern

Bit Manipulation

Approaches

XOR

Code

def singleNumber(nums: list[int]) -> int:
    """Return the element that appears only once."""
    result = 0
    for num in nums:
        result ^= num
    return result

Test

>>> from single_number__xor import singleNumber
>>> singleNumber([2, 2, 1])
1
>>> singleNumber([4, 1, 2, 1, 2])
4
>>> singleNumber([1])
1

single_number__xor.singleNumber(nums: list[int]) → int

Return the element that appears only once.