go位操作

func nagation(a int) int {
	return ^a + 1
}

func swap(a, b int) (int, int) {
	a ^= b
	b ^= a
	a ^= b
	return a, b
}

func even(a int) (array []int) {
	for i := 0; i < a; i++ {
		if i&1 == 0 {
			array = append(array, i)
		}
	}
	return array
}