Given a non-empty array of integers where every element appears exactly twice except for one element that appears once, find that single element.
For example, given [2, 2, 1], the answer is 1. Given [4, 1, 2, 1, 2], the answer is 4.
Explain how you would solve this in O(n) time and O(1) space. What property of a specific bitwise operation makes this possible?
How to approach it
- Hint 1
Think about what happens when you XOR a number with itself.
- Hint 2
XOR has useful properties: a ^ a = 0, a ^ 0 = a, and it is commutative and associative.
- Hint 3
If you XOR all elements together, what survives?
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