func singleNumber(nums []int) []int {
	n, a, b := len(nums), 0, 0
	for i := 0; i < n; i++ {
		a ^= nums[i]
	}
	mask := 1
	for mask & a == 0 {
		mask <<= 1
	}
	a = 0
	for i := 0; i < n; i++ {
		if nums[i] & mask == 0 { // Use the mask to split all nums into 2 groups
			a ^= nums[i]
		} else {
			b ^= nums[i]
		}
	}
	return []int{a, b}
}