python 队列(python队列的使用)

实现队列

class Queue(object):
    def __init__(self):
        self._queue=[]
    
    def push(self,data):
        self._queue.append(data)
        
    def pop(self):
        if self._queue:
            peek=self._queue[0]
            self._queue=self._queue[1:]
            return peek
        else:
            return None
        
    def front(self):
        if self._queue:
            return self._queue[0]
        else:
            return None
        
    def is_empty(self):
        return self._queue==[]
    
    def size(self):
        return len(self._queue)

扩展：

（1）用两个队列实现一个栈

class Stack(object):
    def __init__(self):
        self._queue1 = Queue()
        self._queue2 = Queue()

    def push(self, data):
        size1 = self._queue1.size()
        size2 = self._queue2.size()
        if size1 and size2:
            self._queue2.push(self._queue1.pop())
            self._queue2.push(data)
        elif size1 == 0:
            self._queue2.push(data)
        elif size2 == 0:
            self._queue1.push(data)

    def pop(self):
        size1 = self._queue1.size()
        size2 = self._queue2.size()
        while size1 > 1:
            self._queue2.push(self._queue1.pop())
            size1 -= 1
        if size1 == 1:
            return self._queue1.pop()
        while size2 > 1:
            self._queue1.push(self._queue2.pop())
            size2 -= 1
        if size2 == 1:
            return self._queue2.pop()
        return None