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  • Implement Stack using Queues ——LeetCode

    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).

    题目大意:用队列,实现栈。

    class MyStack {
        
        List<Integer> stack = new ArrayList<>();
        
        // Push element x onto stack.
        public void push(int x) {
            stack.add(x);
        }
    
        // Removes the element on top of the stack.
        public void pop() {
            if(!empty()){
                stack.remove(stack.size()-1);
            }
        }
    
        // Get the top element.
        public int top() {
            if(!empty()){
                return stack.get(stack.size()-1);
            }
            return -1;
        }
    
        // Return whether the stack is empty.
        public boolean empty() {
            return stack.size()==0;
        }
    }
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  • 原文地址:https://www.cnblogs.com/aboutblank/p/4599576.html
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