gods/stacks/arraystack/arraystack.go

/*
Copyright (c) 2015, Emir Pasic
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

// Package arraystack implements a stack backed by array list.
//
// Structure is not thread safe.
//
// Reference: https://en.wikipedia.org/wiki/Stack_%28abstract_data_type%29#Array
package arraystack

import (
	"fmt"
	"github.com/emirpasic/gods/containers"
	"github.com/emirpasic/gods/lists/arraylist"
	"github.com/emirpasic/gods/stacks"
	"strings"
)

func assertInterfaceImplementation() {
	var _ stacks.Stack = (*Stack)(nil)
	var _ containers.ReverseIteratorWithIndex = (*Iterator)(nil)
}

// Stack holds elements in an array-list
type Stack struct {
	list *arraylist.List
}

// New instantiates a new empty stack
func New() *Stack {
	return &Stack{list: arraylist.New()}
}

// Push adds a value onto the top of the stack
func (stack *Stack) Push(value interface{}) {
	stack.list.Add(value)
}

// Pop removes top element on stack and returns it, or nil if stack is empty.
// Second return parameter is true, unless the stack was empty and there was nothing to pop.
func (stack *Stack) Pop() (value interface{}, ok bool) {
	value, ok = stack.list.Get(stack.list.Size() - 1)
	stack.list.Remove(stack.list.Size() - 1)
	return
}

// Peek returns top element on the stack without removing it, or nil if stack is empty.
// Second return parameter is true, unless the stack was empty and there was nothing to peek.
func (stack *Stack) Peek() (value interface{}, ok bool) {
	return stack.list.Get(stack.list.Size() - 1)
}

// Empty returns true if stack does not contain any elements.
func (stack *Stack) Empty() bool {
	return stack.list.Empty()
}

// Size returns number of elements within the stack.
func (stack *Stack) Size() int {
	return stack.list.Size()
}

// Clear removes all elements from the stack.
func (stack *Stack) Clear() {
	stack.list.Clear()
}

// Values returns all elements in the stack (LIFO order).
func (stack *Stack) Values() []interface{} {
	size := stack.list.Size()
	elements := make([]interface{}, size, size)
	for i := 1; i <= size; i++ {
		elements[size-i], _ = stack.list.Get(i - 1) // in reverse (LIFO)
	}
	return elements
}

// Iterator returns a stateful iterator whose values can be fetched by an index.
type Iterator struct {
	stack *Stack
	index int
}

// Iterator returns a stateful iterator whose values can be fetched by an index.
func (stack *Stack) Iterator() Iterator {
	return Iterator{stack: stack, index: -1}
}

// Next moves the iterator to the next element and returns true if there was a next element in the container.
// If Next() returns true, then next element's index and value can be retrieved by Index() and Value().
// If Next() was called for the first time, then it will point the iterator to the first element if it exists.
// Modifies the state of the iterator.
func (iterator *Iterator) Next() bool {
	if iterator.index < iterator.stack.Size() {
		iterator.index++
	}
	return iterator.stack.withinRange(iterator.index)
}

// Prev moves the iterator to the previous element and returns true if there was a previous element in the container.
// If Prev() returns true, then previous element's index and value can be retrieved by Index() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator) Prev() bool {
	if iterator.index >= 0 {
		iterator.index--
	}
	return iterator.stack.withinRange(iterator.index)
}

// Value returns the current element's value.
// Does not modify the state of the iterator.
func (iterator *Iterator) Value() interface{} {
	value, _ := iterator.stack.list.Get(iterator.stack.list.Size() - iterator.index - 1) // in reverse (LIFO)
	return value
}

// Index returns the current element's index.
// Does not modify the state of the iterator.
func (iterator *Iterator) Index() int {
	return iterator.index
}

// Begin resets the iterator to its initial state (one-before-first)
// Call Next() to fetch the first element if any.
func (iterator *Iterator) Begin() {
	iterator.index = -1
}

// End moves the iterator past the last element (one-past-the-end).
// Call Prev() to fetch the last element if any.
func (iterator *Iterator) End() {
	iterator.index = iterator.stack.Size()
}

// First moves the iterator to the first element and returns true if there was a first element in the container.
// If First() returns true, then first element's index and value can be retrieved by Index() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator) First() bool {
	iterator.Begin()
	return iterator.Next()
}

// Last moves the iterator to the last element and returns true if there was a last element in the container.
// If Last() returns true, then last element's index and value can be retrieved by Index() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator) Last() bool {
	iterator.End()
	return iterator.Prev()
}

// String returns a string representation of container
func (stack *Stack) String() string {
	str := "ArrayStack\n"
	values := []string{}
	for _, value := range stack.list.Values() {
		values = append(values, fmt.Sprintf("%v", value))
	}
	str += strings.Join(values, ", ")
	return str
}

// Check that the index is within bounds of the list
func (stack *Stack) withinRange(index int) bool {
	return index >= 0 && index < stack.list.Size()
}