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  • 练习题 (六)

    题目:

    Implement Stack using Queues

    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 backpeek/pop from frontsize, 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).

    解答:

    class Stack:
    
        # initialize your data structure here.
        def __init__(self):
            self.stack = []
    
        # @param x, an integer
        # @return nothing
        def push(self, x):
            self.stack.append(x)
    
        # @return nothing
        def pop(self):
            if len(self.stack) == 0:
                print 'can not pop from an empty stack !'
            else:
                self.stack.pop()
    
        # @return an integer
        def top(self):
            if len(self.stack) == 0:
                return None
            value = self.stack.pop()
            self.stack.append(value)
            return value
    
        # @return an boolean
        def empty(self):
            if len(self.stack) == 0:
                return True
            else:
                return False

    心得:

    List现在已经可以模拟stack或者sequence, 这里题目明确说明可以使用list, 所以就用list.

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  • 原文地址:https://www.cnblogs.com/ender-cd/p/4615689.html
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