Single Number

Single Number is a Easy Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Bit Manipulation Patterns pattern, in the Bitwise XOR - Finding Single/Missing Number subpattern.

Problem statement

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.

Topics and companies

Topics: Array, Bit Manipulation.

Reported in interviews at Google, Amazon, Facebook, Microsoft.

How to practise Single Number on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(n) time and O(1) space.

Open Single Number in the code editor, or read the Single Number editorial for a worked solution with its approach and complexity analysis.

Where Single Number sits in the DSA pattern sheet

• Bit Manipulation Patterns pattern guide
• Bitwise XOR - Finding Single/Missing Number subpattern
• The full DSA patterns sheet
• All coding practice problems

Problems related to Single Number

Other problems that use the same Bitwise XOR - Finding Single/Missing Number and Bit Manipulation Patterns techniques:

• Find the Difference — Easy, same subpattern
• Missing Number — Easy, same subpattern
• Single Number II — Medium, same subpattern
• Counting Bits — Easy, same pattern
• Number of 1 Bits — Easy, same pattern
• Power of Four — Easy, same pattern