• leetcode 232. Implement Queue using Stacks


    Implement the following operations of a queue using stacks.

    • push(x) -- Push element x to the back of queue.
    • pop() -- Removes the element from in front of queue.
    • peek() -- Get the front element.
    • empty() -- Return whether the queue is empty.

    Example:

    MyQueue queue = new MyQueue();
    
    queue.push(1);
    queue.push(2);  
    queue.peek();  // returns 1
    queue.pop();   // returns 1
    queue.empty(); // returns false

    Notes:

    • You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
    • Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
    • You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).
    class MyQueue:
    
        def __init__(self):
            """
            Initialize your data structure here.
            """
            self.stack1 = []
            self.stack2 = []
            
    
        def push(self, x):
            """
            Push element x to the back of queue.
            :type x: int
            :rtype: void
            """
            self.stack1.append(x)
        
        def dump_data(self):
            if not self.stack2:
                while self.stack1:
                    self.stack2.append(self.stack1.pop())
    
        def pop(self):
            """
            Removes the element from in front of queue and returns that element.
            :rtype: int
            """
            self.dump_data()
            return self.stack2.pop()
            
    
        def peek(self):
            """
            Get the front element.
            :rtype: int
            """
            self.dump_data()
            return self.stack2[-1]
            
    
        def empty(self):
            """
            Returns whether the queue is empty.
            :rtype: bool
            """
            return not self.stack1 and not self.stack2
    
    
    # Your MyQueue object will be instantiated and called as such:
    # obj = MyQueue()
    # obj.push(x)
    # param_2 = obj.pop()
    # param_3 = obj.peek()
    # param_4 = obj.empty()
    
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  • 原文地址:https://www.cnblogs.com/bonelee/p/9180422.html
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