栈和队列理论基础

• 队列是先进先出，栈是先进后出

LeetCode题目

232.用栈实现队列

题目链接：Implement Queue using Stacks - LeetCode

代码如下：

type MyStack []int

func (s *MyStack) Push(v int) {
	*s = append(*s, v)
}

func (s *MyStack) Pop() int {
	val := (*s)[len(*s)-1]
	*s = (*s)[:len(*s)-1]
	return val
}

func (s *MyStack) Peek() int {
	return (*s)[len(*s)-1]
}

func (s *MyStack) Size() int {
	return len(*s)
}

func (s *MyStack) Empty() bool {
	return s.Size() == 0
}

type MyQueue struct {
	stackIn  *MyStack
	stackOut *MyStack
}

func Constructor() MyQueue {
	return MyQueue{
		stackIn:  &MyStack{},
		stackOut: &MyStack{},
	}
}

func (this *MyQueue) fillStackOut() {
	if this.stackOut.Empty() {
		for !this.stackIn.Empty() {
			val := this.stackIn.Pop()
			this.stackOut.Push(val)
		}
	}
}

func (this *MyQueue) Push(x int) {
	this.stackIn.Push(x)
}

func (this *MyQueue) Pop() int {
	this.fillStackOut()
	return this.stackOut.Pop()
}

func (this *MyQueue) Peek() int {
	this.fillStackOut()
	return this.stackOut.Peek()
}

func (this *MyQueue) Empty() bool {
	return this.stackIn.Empty() && this.stackOut.Empty()
}

225.用队列实现栈

题目链接：Implement Stack using Queues - LeetCode

代码如下：

type MyStack struct {
	queue1 []int
	queue2 []int
}

func Constructor() MyStack {
	return MyStack{
		queue1: make([]int, 0),
		queue2: make([]int, 0),
	}
}

func (this *MyStack) Move() {
	if len(this.queue1) == 0 {
		this.queue1, this.queue2 = this.queue2, this.queue1
	} else {
		this.queue2 = append(this.queue2, this.queue1[0])
		this.queue1 = this.queue1[1:]
		this.Move()
	}
}

func (this *MyStack) Push(x int) {
	this.queue2 = append(this.queue2, x)
	this.Move()
}

func (this *MyStack) Pop() int {
	val := this.queue1[0]
	this.queue1 = this.queue1[1:]
	return val
}

func (this *MyStack) Top() int {
	return this.queue1[0]
}

func (this *MyStack) Empty() bool {
	return len(this.queue1) == 0
}