题解 | 【模板】队列

from collections import deque


class Queue:
    def __init__(self):
        self.items = deque()

    def push(self, x):
        """将x加入队尾"""
        self.items.append(x)

    def pop(self):
        """输出并移除队首元素"""
        if not self.items:
            return "error"
        return self.items.popleft()

    def front(self):
        """输出队首元素（不移除）"""
        if not self.items:
            return "error"
        return self.items[0]


# 处理输入输出
n = int(input())
queue = Queue()

for _ in range(n):
    operation = input().strip().split()
    if operation[0] == "push":
        x = int(operation[1])
        queue.push(x)
    elif operation[0] == "pop":
        print(queue.pop())
    elif operation[0] == "front":
        print(queue.front())