Single Number

Problem

Every element of nums appears exactly twice except for one element that appears once; return that unique value.

XOR all the numbers together so duplicate pairs cancel to 0 and the odd one out survives. Runs in O(n) time with O(1) extra space.

Hint

XOR is associative and commutative, so the order of cancellation does not matter.

case 1

in: [[2,2,1]]

expected: 1

case 2

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

expected: 4

case 3

in: [[1]]

expected: 1

case 4

in: [[-1,-1,-2]]

expected: -2

case 5

in: [[0,0,5]]

expected: 5

Starter codePython

def single_number(nums):
    # Your code here
    pass

5 test cases · run your code against them in the editor