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232_stacktoqueue.go
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232_stacktoqueue.go
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/*
Implement the following operations of a queue using stacks.
push(x) -- Push element x to the back of queue.
pop() -- Removes the element from in front of queue.
peek() -- Get the front element.
empty() -- Return whether the queue is empty.
Example:
MyQueue queue = new MyQueue();
queue.push(1);
queue.push(2);
queue.peek(); // returns 1
queue.pop(); // returns 1
queue.empty(); // returns false
Notes:
You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).
*/
/*
#### 解题思路
- 使用两个栈进行实现,一个in,一个out,所有元素从栈in进入,当元素出去时,先看out栈是否有值,有的话直接pop
- 若out栈为空,从in栈依次将值抛出并压入out栈,再从out栈取值从而达到先入先出的效果
*/
package main
type Stack struct {
s []int
}
func NewStack() *Stack {
return &Stack{}
}
func (s *Stack) Push(x int) {
s.s = append(s.s, x)
}
func (s Stack) Peek() int {
return s.s[len(s.s)-1]
}
func (s *Stack) Pop() int {
t := s.Peek()
s.s = s.s[:len(s.s)-1]
return t
}
func (s Stack) Size() int {
return len(s.s)
}
func (s Stack) Empty() bool {
return len(s.s) == 0
}
type MyQueue struct {
stackIn *Stack
stackOut *Stack
}
/** Initialize your data structure here. */
func Constructor() MyQueue {
return MyQueue{stackIn: NewStack(), stackOut: NewStack()}
}
/** Push element x to the back of queue. */
func (this *MyQueue) Push(x int) {
this.stackIn.Push(x)
}
/** Removes the element from in front of queue and returns that element. */
func (this *MyQueue) Pop() int {
if this.stackOut.Empty() {
for !this.stackIn.Empty() {
this.stackOut.Push(this.stackIn.Pop())
}
}
return this.stackOut.Pop()
}
/** Get the front element. */
func (this *MyQueue) Peek() int {
if this.stackOut.Empty() {
for !this.stackIn.Empty() {
this.stackOut.Push(this.stackIn.Pop())
}
}
return this.stackOut.Peek()
}
/** Returns whether the queue is empty. */
func (this *MyQueue) Empty() bool {
return this.stackOut.Empty() && this.stackIn.Empty()
}