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232. Implement Queue using Stacks

时间:2017-10-24 22:44:24      阅读:217      评论:0      收藏:0      [点我收藏+]

标签:init   bool   boolean   logs   div   nbsp   ret   standard   move   

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 toppeek/pop from topsize, and is emptyoperations 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).

题目含义:使用stack来实现queue的功能

 1 class MyQueue {
 2     Stack<Integer> input = new Stack();
 3     Stack<Integer> output = new Stack();
 4     /** Initialize your data structure here. */
 5     public MyQueue() {
 6         
 7     }
 8     
 9     /** Push element x to the back of queue. */
10     public void push(int x) {
11         input.push(x);     
12     }
13     
14     /** Removes the element from in front of queue and returns that element. */
15     public int pop() {
16              peek();
17         return output.pop();   
18     }
19     
20     /** Get the front element. */
21     public int peek() {
22         if (output.empty())
23             while (!input.empty())
24                 output.push(input.pop());
25         return output.peek();
26         
27     }
28     
29     /** Returns whether the queue is empty. */
30     public boolean empty() {
31          return input.empty() && output.empty();
32     }
33 }

 

232. Implement Queue using Stacks

标签:init   bool   boolean   logs   div   nbsp   ret   standard   move   

原文地址:http://www.cnblogs.com/wzj4858/p/7725664.html

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