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99 lines
2.3 KiB
Markdown
99 lines
2.3 KiB
Markdown
# [232. Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks/)
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## 题目
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Implement the following operations of a queue using stacks.
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- push(x) -- Push element x to the back of queue.
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- pop() -- Removes the element from in front of queue.
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- peek() -- Get the front element.
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- empty() -- Return whether the queue is empty.
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**Example**:
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```
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MyQueue queue = new MyQueue();
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queue.push(1);
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queue.push(2);
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queue.peek(); // returns 1
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queue.pop(); // returns 1
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queue.empty(); // returns false
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```
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**Note**:
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- 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.
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- 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.
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- You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).
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## 题目大意
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题目要求用栈实现一个队列的基本操作：push(x)、pop()、peek()、empty()。
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## 解题思路
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按照题目要求实现即可。
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## 代码
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```go
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package leetcode
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type MyQueue struct {
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Stack *[]int
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Queue *[]int
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}
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/** Initialize your data structure here. */
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func Constructor232() MyQueue {
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tmp1, tmp2 := []int{}, []int{}
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return MyQueue{Stack: &tmp1, Queue: &tmp2}
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}
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/** Push element x to the back of queue. */
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func (this *MyQueue) Push(x int) {
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*this.Stack = append(*this.Stack, x)
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}
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/** Removes the element from in front of queue and returns that element. */
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func (this *MyQueue) Pop() int {
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if len(*this.Queue) == 0 {
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this.fromStackToQueue(this.Stack, this.Queue)
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}
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popped := (*this.Queue)[len(*this.Queue)-1]
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*this.Queue = (*this.Queue)[:len(*this.Queue)-1]
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return popped
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}
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/** Get the front element. */
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func (this *MyQueue) Peek() int {
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if len(*this.Queue) == 0 {
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this.fromStackToQueue(this.Stack, this.Queue)
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}
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return (*this.Queue)[len(*this.Queue)-1]
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}
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/** Returns whether the queue is empty. */
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func (this *MyQueue) Empty() bool {
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return len(*this.Stack)+len(*this.Queue) == 0
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}
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func (this *MyQueue) fromStackToQueue(s, q *[]int) {
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for len(*s) > 0 {
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popped := (*s)[len(*s)-1]
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*s = (*s)[:len(*s)-1]
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*q = append(*q, popped)
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}
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}
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``` |