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  • *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).

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

    class MyStack {
        Queue<Integer> queue = new LinkedList<Integer>();
        
        // Push element x onto stack.
        public void push(int x) 
        {
            queue.add(x);
            int n = queue.size();
            while(n>1)
            {
                queue.add(queue.poll());
                n--;
            }
            
        }
    
        // Removes the element on top of the stack.
        public void pop() {
            queue.poll();
        }
    
        // Get the top element.
        public int top() {
            return queue.peek();
        }
    
        // Return whether the stack is empty.
        public boolean empty() {
            return queue.isEmpty();
        }
    }
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  • 原文地址:https://www.cnblogs.com/hygeia/p/5126120.html
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