evaluate-reverse-polish-notation.go

func pop(alist *[]int) int {
	f := len(*alist)
	rv := (*alist)[f-1]
	*alist = append((*alist)[:f-1])
	return rv
}

func calc(b int, a int, f string) int {

	if f == "/" {
		return a / b
	}
	if f == "+" {
		return a + b
	}
	if f == "-" {
		return a - b
	}
	if f == "*" {
		return a * b
	}

	return 0
}

func evalRPN(tokens []string) int {

	st := make([]int, 0)
	for _, j := range tokens {

		jj, err := strconv.Atoi(j)

		if err != nil {
			a := pop(&st)
			b := pop(&st)
			st = append(st, calc(a, b, j))
		} else {
			st = append(st, jj)
		}
		
	}

	return st[0]
}