describe

Implement a last in first out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal queue (push, top, pop, and empty).

Implement the MyStack class:

  • void push(int x) Pushes element x to the top of the stack.
  • int pop() Removes the element on the top of the stack and returns it.
  • int top() Returns the element on the top of the stack.
  • boolean empty() Returns true if the stack is empty, false otherwise.

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, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue), as long as you use only a queue’s standard operations.

Example 1:

Input
["MyStack", "push", "push", "top", "pop", "empty"]
[[], [1], [2], [], [], []]
Output
[null, null, null, 2, 2, false]

Explanation
MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // return 2
myStack.pop(); // return 2
myStack.empty(); // return False	
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Note:

1 <= x <= 9
At most 100 calls will be made to push, pop, top, and empty.
All the calls to pop and top are valid.
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parsing

According to the question, it means to construct each function according to the question, the idea is very simple, it is the basic operation of the list, there is nothing to explain.

answer

class MyStack(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.stack = []

    def push(self, x):
        """
        Push element x onto stack.
        :type x: int
        :rtype: None
        """
        self.stack.append(x)

    def pop(self):
        """
        Removes the element on top of the stack and returns that element.
        :rtype: int
        """
        if self.stack:
            return self.stack.pop(-1)
        return None

    def top(self):
        """
        Get the top element.
        :rtype: int
        """
        if self.stack:
            return self.stack[-1]
        return None

    def empty(self):
        """
        Returns whether the stack is empty.
        :rtype: bool
        """
        if not self.stack:
            return True
        return False
        
        	      
		
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The results

Given the linked list in Python online submissions for implementing Stack using Queues. Memory Usage: The linked list is given in the linked list in Python online submissions for Implement Stack using Queues.Copy the code

Original link: leetcode.com/problems/im…

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