Single Number

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Problem

Given a non-empty array of integers where every element appears exactly twice except for one, find that single element, using linear time and constant extra space.

Examples

Example 1

Input:nums = [2,2,1]

Output:1

Example 2

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

Output:4

Constraints

1 <= nums.length <= 3 * 10^4

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How to approach it: the Bit Manipulation pattern

Work directly on a number's binary representation using bitwise operators — often turning an O(n) or O(log n) problem into a handful of O(1) operations.

Look for this pattern when

The problem talks about bits directly (count set bits, reverse bits, single number among duplicates).
You want a constant-time trick instead of a loop for a numeric problem.

Read the full Bit Manipulation guide →

Video walkthroughs

Original problem on LeetCode ↗