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Problem

Single Number

LeetCode #136Easy
XOR fold · pairs cancel

Given a non-empty array where every element appears twice except for one, find that single one using O(1) extra space.

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Brute · hash count
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1count ← {}
2for x in nums: count[x]++
3return the key with count == 1
state
  • nums[4, 1, 2, 1, 2]

line 1Every value appears exactly twice except one. Obvious approach: count occurrences in a hash map and return the value seen once.