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  • Java [Leetcode 232]Implement Queue using Stacks

    题目描述:

    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 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).

    解题思路:

    使用两个stack,一个用于插入数据,另一个用于输出数据。

    代码如下:

    class MyQueue {
        Stack<Integer> input = new Stack<Integer>();
        Stack<Integer> output = new Stack<Integer>();
        // Push element x to the back of queue.
        public void push(int x) {
            input.push(x);
        }
    
        // Removes the element from in front of queue.
        public void pop() {
            peek();
            output.pop();
        }
    
        // Get the front element.
        public int peek() {
            if(output.empty()){
                while(!input.empty()){
                    output.push(input.pop());
                }
            }
            return output.peek();
        }
    
        // Return whether the queue is empty.
        public boolean empty() {
            return input.empty() && output.empty();
        }
    }
    

      

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  • 原文地址:https://www.cnblogs.com/zihaowang/p/5102210.html
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