easy

Single Number

In a non-empty integer array every element appears exactly twice except one, which appears once. Find that element in linear time using constant extra memory.

Constraints

1 ≤ n ≤ 3 · 10^4
-3 · 10^4 ≤ nums[i] ≤ 3 · 10^4
Exactly one element appears once

Examples

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

out: 4

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