232用栈实现队列
https://leetcode-cn.com/problems/implement-queue-using-stacks/
代码：
class MyQueue {
private Stack<Integer> inStack;
private Stack<Integer> outStack;
/** Initialize your data structure here. */
public MyQueue() {
inStack = new Stack<>();
outStack = new Stack<>();
}
/** Push element x to the back of queue. */
public void push(int x) {
inStack.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
if(!outStack.isEmpty()){
return outStack.pop();
}
while(!inStack.isEmpty()){
outStack.push(inStack.pop());
}
return outStack.pop();
}
/** Get the front element. */
public int peek() {
if(!outStack.isEmpty()){
return outStack.peek();
}
while(!inStack.isEmpty()){
outStack.push(inStack.pop());
}
return outStack.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
return outStack.isEmpty()&&inStack.isEmpty();
}
}
/**
* Your MyQueue object will be instantiated and called as such:
* MyQueue obj = new MyQueue();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.peek();
* boolean param_4 = obj.empty();
*/
