// Dijkstra's Two-Stack Algorithm for Expression Evaluation
// $ ./evaluate
// ( 1 + ( ( 2 + 3 ) * ( 4 * 5 ) ) )
// 101.0
// $ ./evaluate
// ( ( 1 + sqrt ( 5.0 ) ) / 2.0 )
// 1.618033988749895
func main() {
ops := stack.NewLinked()
vals := stack.NewLinked()
stdin := stdin.NewStdin()
for !stdin.IsEmpty() {
s, _ := stdin.ReadString()
if s == "(" {
// ignore...
} else if s == "+" {
ops.Push(s)
} else if s == "-" {
ops.Push(s)
} else if s == "*" {
ops.Push(s)
} else if s == "/" {
ops.Push(s)
} else if s == "sqrt" {
ops.Push(s)
} else if s == ")" {
// Pop, evaluate, and push result if token is ")"
var value float64
op, _ := ops.Pop()
v, _ := vals.Pop()
if op == "+" {
v1, _ := vals.Pop()
value = v1.(float64) + v.(float64)
} else if op == "-" {
v1, _ := vals.Pop()
value = v1.(float64) - v.(float64)
} else if op == "*" {
v1, _ := vals.Pop()
value = v1.(float64) * v.(float64)
} else if op == "/" {
v1, _ := vals.Pop()
value = v1.(float64) / v.(float64)
} else if op == "sqrt" {
value = math.Sqrt(v.(float64))
}
vals.Push(value)
} else {
// Token not operator or paren: push value
value, _ := strconv.ParseFloat(s, 64)
vals.Push(value)
}
}
result, _ := vals.Pop()
fmt.Println(result.(float64))
}
/*************************************************************************
* Execution: ./stack < input.txt
*
* % more tobe.txt
* to be or not to - be - - that - - - is
*
* % ./stack < tobe.txt
* to be not that or be (2 left on stack)
*
*************************************************************************/
func main() {
s := stack.NewLinked()
stdin := stdin.NewStdin()
for !stdin.IsEmpty() {
item, _ := stdin.ReadString()
if item != "-" {
s.Push(item)
} else if !s.IsEmpty() {
item, _ := s.Pop()
fmt.Printf("%s ", item)
}
}
fmt.Printf("(%d left on stack)\n", s.Size())
}
