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website/content/ChapterFour/0232.Implement-Queue-using-Stacks.md

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+# [232. Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks/)
+
+## 题目
+
+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
+
+```
+
+**Note**:  
+
+- 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).
+ 
+
+## 题目大意
+
+题目要求用栈实现一个队列的基本操作：push(x)、pop()、peek()、empty()。
+
+## 解题思路
+
+按照题目要求实现即可。
+
+
+
+## 代码
+
+```go
+
+package leetcode
+
+type MyQueue struct {
+	Stack *[]int
+	Queue *[]int
+}
+
+/** Initialize your data structure here. */
+func Constructor232() MyQueue {
+	tmp1, tmp2 := []int{}, []int{}
+	return MyQueue{Stack: &tmp1, Queue: &tmp2}
+}
+
+/** Push element x to the back of queue. */
+func (this *MyQueue) Push(x int) {
+	*this.Stack = append(*this.Stack, x)
+}
+
+/** Removes the element from in front of queue and returns that element. */
+func (this *MyQueue) Pop() int {
+	if len(*this.Queue) == 0 {
+		this.fromStackToQueue(this.Stack, this.Queue)
+	}
+
+	popped := (*this.Queue)[len(*this.Queue)-1]
+	*this.Queue = (*this.Queue)[:len(*this.Queue)-1]
+	return popped
+}
+
+/** Get the front element. */
+func (this *MyQueue) Peek() int {
+	if len(*this.Queue) == 0 {
+		this.fromStackToQueue(this.Stack, this.Queue)
+	}
+
+	return (*this.Queue)[len(*this.Queue)-1]
+}
+
+/** Returns whether the queue is empty. */
+func (this *MyQueue) Empty() bool {
+	return len(*this.Stack)+len(*this.Queue) == 0
+}
+
+func (this *MyQueue) fromStackToQueue(s, q *[]int) {
+	for len(*s) > 0 {
+		popped := (*s)[len(*s)-1]
+		*s = (*s)[:len(*s)-1]
+
+		*q = append(*q, popped)
+	}
+}
+
+```