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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).
一个队列即可完成，上代码： 

class MyStack {
    
    LinkedList<Integer> queue = new LinkedList<Integer>();
    
	// Push element x onto stack.
    public void push(int x) {
        queue.add(x);
        for (int i = 0; i < queue.size()-1; i++) {
            queue.add(queue.poll());
        }
    }

    // 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();
    }
}

主要是每次push的时候，其实已经把入队列的顺序给reverse了。用两个队列也可以实现，但是复杂程度实在是太高了，就不展示了




本文标签： implementLeetCodequeuesStack

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