# leetcode232 Implement Queue using Stacks

## 题目要求

``````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.
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).``````

## 思路与代码

1.输入[1,2,3,4,5]

2.获得捅底的元素1，则将1号桶导入2号桶，获取元素后再倒回

3.输入[6]

4.获得当前捅底的元素2，那么操作同第二步

1.输入[1,2,3,4,5]

2.弹出1

3.弹出2

4.输入[6,7]

``````public class ImplementQueueusingStacks_232 {
Stack<Integer> s1 = new Stack<Integer>();
Stack<Integer> s2 = new Stack<Integer>();
/** Push element x to the back of queue. */
public void push(int x) {
s1.push(x);
}

/** Removes the element from in front of queue and returns that element. */
public int pop() {
if(s2.isEmpty()){
while(!s1.isEmpty()){
s2.push(s1.pop());
}
}
return s2.pop();
}

/** Get the front element. */
public int peek() {
if(s2.isEmpty()){
while(!s1.isEmpty()){
s2.push(s1.pop());
}
}
return s2.peek();
}

/** Returns whether the queue is empty. */
public boolean empty() {
return s1.empty() && s2.empty();
}
}
``````

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