Leetcode 225 Implement Stack using Queues

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Implement the following operations of a stack using queues.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• empty() -- Return whether the stack is empty.

Notes:

• You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, and is empty operations are valid.
• Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
• You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

Update (2015-06-11):
The class name of the Java function had been updated to MyStack instead of Stack.

class Stack
    # Initialize your data structure here.
    def initialize
        @q = Array.new
    end

    # @param {Integer} x
    # @return {void}
    def push(x)
        @q << x
    end

    # @return {void}
    def pop
       (@q.length-1).times {@q << @q.shift}
       @q.shift
    end

    # @return {Integer}
    def top
        (@q.length-1).times {@q << @q.shift}
        t = @q.shift
        @q << t
        t
    end

    # @return {Boolean}
    def empty
        @q.empty?
    end
end

Leetcode 225 Implement Stack using Queues

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原文地址：http://www.cnblogs.com/lilixu/p/4571013.html