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Single Number

Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.
You must implement a solution with a linear runtime complexity and use only constant extra space.

Solve on Leetcode

Solution in Go

func singleNumber(nums []int) int {
	count := make(map[int]int, (len(nums)/2)+1)
	result := 0

	for _, n := range nums {
		count[n]++

		c := count[n]
		if c == 1 {
			result += n
		} else {
			result -= n
		}
	}

	return result
}

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The Go gopher was designed by Renee French.