[AL&DS] 스택

type Stack []interface{}

// 스택 (LIFO)
func (s *Stack) addStack(_appendNum int) Stack {
	*s = append(*s, _appendNum)
	return *s
}

func (s *Stack) removeStack() interface{} {
	if len(*s) < 0 {
		return 0
	}
	topIdx := len(*s) - 1
	data := (*s)[topIdx]
	*s = (*s)[:topIdx]

	// fmt.Println(*s)
	return data
}