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114 lines
2.1 KiB
Go
114 lines
2.1 KiB
Go
// Copyright 2017 The OPA Authors. All rights reserved.
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// Use of this source code is governed by an Apache2
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// license that can be found in the LICENSE file.
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package util
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// LIFO represents a simple LIFO queue.
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type LIFO struct {
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top *queueNode
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size int
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}
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type queueNode struct {
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v T
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next *queueNode
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}
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// NewLIFO returns a new LIFO queue containing elements ts starting with the
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// left-most argument at the bottom.
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func NewLIFO(ts ...T) *LIFO {
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s := &LIFO{}
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for i := range ts {
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s.Push(ts[i])
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}
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return s
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}
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// Push adds a new element onto the LIFO.
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func (s *LIFO) Push(t T) {
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node := &queueNode{v: t, next: s.top}
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s.top = node
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s.size++
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}
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// Peek returns the top of the LIFO. If LIFO is empty, returns nil, false.
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func (s *LIFO) Peek() (T, bool) {
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if s.top == nil {
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return nil, false
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}
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return s.top.v, true
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}
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// Pop returns the top of the LIFO and removes it. If LIFO is empty returns
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// nil, false.
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func (s *LIFO) Pop() (T, bool) {
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if s.top == nil {
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return nil, false
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}
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node := s.top
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s.top = node.next
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s.size--
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return node.v, true
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}
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// Size returns the size of the LIFO.
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func (s *LIFO) Size() int {
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return s.size
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}
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// FIFO represents a simple FIFO queue.
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type FIFO struct {
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front *queueNode
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back *queueNode
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size int
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}
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// NewFIFO returns a new FIFO queue containing elements ts starting with the
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// left-most argument at the front.
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func NewFIFO(ts ...T) *FIFO {
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s := &FIFO{}
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for i := range ts {
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s.Push(ts[i])
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}
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return s
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}
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// Push adds a new element onto the LIFO.
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func (s *FIFO) Push(t T) {
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node := &queueNode{v: t, next: nil}
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if s.front == nil {
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s.front = node
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s.back = node
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} else {
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s.back.next = node
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s.back = node
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}
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s.size++
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}
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// Peek returns the top of the LIFO. If LIFO is empty, returns nil, false.
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func (s *FIFO) Peek() (T, bool) {
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if s.front == nil {
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return nil, false
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}
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return s.front.v, true
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}
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// Pop returns the top of the LIFO and removes it. If LIFO is empty returns
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// nil, false.
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func (s *FIFO) Pop() (T, bool) {
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if s.front == nil {
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return nil, false
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}
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node := s.front
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s.front = node.next
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s.size--
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return node.v, true
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}
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// Size returns the size of the LIFO.
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func (s *FIFO) Size() int {
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return s.size
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}
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