leetcode-go/easy/645.set-mismatch.go

func findErrorNums(nums []int) []int {
	res := make([]int, 2)
	for i := range nums {
		v := abs(nums[i])
		res[1] += v
		if nums[v-1] < 0 {
			res[0] = v
		}
		nums[v-1] *= -1
	}
	n := len(nums)
	res[1] = (1+n)*n/2 - res[1] + res[0]
	return res
}

func abs(x int) int {
	if x < 0 {
		return -x
	}
	return x
}