题解 | 【模板】队列操作 | Python

n=int(input())
nums=[]
for _ in range(n):
    k=list(map(int,input().split()))
    op=k[0]
    if op==1:
        nums.append(k[1])
    elif op==2:
        if len(nums)==0:
            print('ERR_CANNOT_POP')
        else:
            nums.pop(0)
    elif op==3:
        if len(nums)==0:
            print('ERR_CANNOT_QUERY')
        else:
            print(nums[0])
    else:
        print(len(nums))