Reduce alllocations done by the stack

util/stack.go

@@ -1,49 +1,47 @@
 package util
 
-type (
-	Stack struct {
-		top    *StackNode
-		length int
-	}
-	StackNode struct {
-		value interface{}
-		prev  *StackNode
-	}
-)
+type Stack struct {
+	stA [20]interface{}
+	st  []interface{}
+	top int
+}
 
 // Create a new Stack
 func NewStack() *Stack {
-	return &Stack{nil, 0}
+	s := &Stack{top: -1}
+	s.st = s.stA[:0]
+	return s
 }
 
 // Return the number of items in the Stack
-func (this *Stack) Len() int {
-	return this.length
+func (s *Stack) Len() int {
+	return (s.top + 1)
 }
 
 // View the top item on the Stack
-func (this *Stack) Peek() interface{} {
-	if this.length == 0 {
-		return nil
+func (s *Stack) Peek() interface{} {
+	if s.top == -1 {
+		return -1
 	}
-	return this.top.value
+	return s.st[s.top]
 }
 
 // Pop the top item of the Stack and return it
-func (this *Stack) Pop() interface{} {
-	if this.length == 0 {
-		return nil
+func (s *Stack) Pop() interface{} {
+	if s.top == -1 {
+		return -1
 	}
 
-	n := this.top
-	this.top = n.prev
-	this.length--
-	return n.value
+	s.top--
+	return s.st[(s.top + 1)]
 }
 
 // Push a value onto the top of the Stack
-func (this *Stack) Push(value interface{}) {
-	n := &StackNode{value, this.top}
-	this.top = n
-	this.length++
+func (s *Stack) Push(value interface{}) {
+	s.top++
+	if len(s.st) <= s.top {
+		s.st = append(s.st, value)
+	} else {
+		s.st[s.top] = value
+	}
 }