【python刷题】栈实现队列

栈实现队列

class Queue:
    def __init__(self):
        self.s1 = []
        self.s2 = []

    def peek(self):
        if not self.s2:
            while self.s1:
                self.s2.append(self.s1.pop())
        return self.s2[-1]


    def push(self, x):
        self.s1.append(x)

    def pop(self):
        self.peek()
        if not self.s2:
            return None
        self.s2.pop()

    def empty(self):
        return not self.s1 and not self.s2

queue = Queue()
queue.push(1)
queue.push(2)
queue.push(3)
print("s1:", queue.s1)
print("s2:", queue.s2)
t = queue.peek()
print(t)
print("s1:", queue.s1)
print("s2:", queue.s2)
queue.pop()
print("s1:", queue.s1)
print("s2:", queue.s2)
queue.push(4)
queue.push(5)
print("s1:", queue.s1)
print("s2:", queue.s2)
queue.pop()
print("s1:", queue.s1)
print("s2:", queue.s2)
t = queue.peek()
print(t)
print("s1:", queue.s1)
print("s2:", queue.s2)

结果：
s1: [1, 2, 3]
s2: []
1
s1: []
s2: [3, 2, 1]
s1: []
s2: [3, 2]
s1: [4, 5]
s2: [3, 2]
s1: [4, 5]
s2: [3]
3
s1: [4, 5]
s2: [3]