非独立思考

    1. class MyQueue {
    2.     Stack<Integer> inStack;
    3.     Stack<Integer> outStack;
    5.     /**
    6.      * Initialize your data structure here.
    7.      */
    8.     public MyQueue() {
    9.         inStack = new Stack<>();
    10.         outStack = new Stack<>();
    11.     }
    13.     /**
    14.      * Push element x to the back of queue.
    15.      */
    16.     public void push(int x) {
    17.         // push进入的是inStack
    18.         inStack.push(x);
    19.     }
    21.     /**
    22.      * Removes the element from in front of queue and returns that element.
    23.      */
    24.     public int pop() {
    25.         // pop前要先检查：
    26.         // 如果outStack中还有元素，需要等它先pop完毕才能加入新值
    27.         // 要将inStack里的元素一次性放入outStack
    28.         if (outStack.isEmpty()) {
    29.             in2out();
    30.         }
    31.         return outStack.pop();
    32.     }
    34.     /**
    35.      * Get the front element.
    36.      */
    37.     public int peek() {
    38.         // pop前要先检查：
    39.         // 如果outStack中还有元素，需要等它先pop完毕才能加入新值
    40.         // 要将inStack里的元素一次性放入outStack
    41.         if (outStack.isEmpty()) {
    42.             in2out();
    43.         }
    44.         return outStack.peek();
    45.     }
    47.     /**
    48.      * Returns whether the queue is empty.
    49.      */
    50.     public boolean empty() {
    51.         return inStack.empty() && outStack.empty();
    52.     }
    54.     private void in2out() {
    55.         while (!inStack.empty()) {
    56.             outStack.push(inStack.pop());
    57.         }
    58.     }
    59. }