Python 如何设计 Codeforces 交互式评分器

@user2357112的注释正确地描述了它无法工作的原因.当您的管道将第一个脚本的输出发送到评分器时，您没有向第一个脚本发送‘grader.py’的响应.

因此，我们需要做的是建立一种双向沟通.

这里有一个方法可以做到这一点.在评分器中，将您要测试的脚本命名为subprocess，并通过管道与其通信. 我在代码中添加了额外的解释.

1_Guess_the_Number.py和你的一样:

#!/usr/bin/env python3
l, r = 1, 1000000
while l != r:
    mid = (l + r + 1) // 2
    print(mid, flush=True)
    response = input()
    if response == "<":
        r = mid - 1
    else:
        l = mid

print("!", l)

grader.py接受测试文件的名称作为输入，并使用subprocess.Popen执行它:

# !/usr/bin/env python3
import sys
import subprocess

INP = 12

def interactor(n):
    if n > INP:
        return "<"
    return ">="

def decodeBytes(message):
    # Helperfunction to decode the message from stdin
    # guess has the format b'12345\r\n' 
    # rstrip() removes the \r\n, then we decode it as ascii
    return message.rstrip().decode('ascii')

if __name__ == '__main__':
    print(f'The secret answer is: {INP}')

    # get script name:
    name = sys.argv[1]
    print(f'calling script {name}')

    # start script as a subprocess
    p = subprocess.Popen(["python3", name], stdout=subprocess.PIPE, stdin=subprocess.PIPE)
        
    # create iterator to read subsequent guesses
    stdout_iterator = iter(p.stdout.readline, b"")

    # loop over all guesses
    for msg_in in stdout_iterator:

        #msg_in is a byte array, we need to decode it
        guess = decodeBytes(msg_in)
        print(f'got msg: {guess}')

        if guess.startswith("!"):
            final_answer = int(guess.split()[1])
            print(f'The final answer is: {final_answer}')
            if final_answer == INP:
                print('Answer was correct!')
                break
            print('Answer is wrong!')
            break
        
        # we determine the message to send out
        msg_out = interactor(int(guess))
        print(f'send msg: {msg_out}')
        
        # sending it to the scripts stdin. 
        p.stdin.write((msg_out + '\n').encode())
        # we need to flush stdin, to make sure the message is not stuck in a buffer
        p.stdin.flush()

在命令行中，您可以通过以下方式调用评分器

python grader.py 1_Guess_the_Number.py

打印输出为:

The secret answer is: 12
calling script 1_Guess_the_Number.py
got msg: 500001
send msg: <
got msg: 250001
send msg: <
got msg: 125001
send msg: <
got msg: 62501
send msg: <
got msg: 31251
send msg: <
got msg: 15626
send msg: <
got msg: 7813
send msg: <
got msg: 3907
send msg: <
got msg: 1954
send msg: <
got msg: 977
send msg: <
got msg: 489
send msg: <
got msg: 245
send msg: <
got msg: 123
send msg: <
got msg: 62
send msg: <
got msg: 31
send msg: <
got msg: 16
send msg: <
got msg: 8
send msg: >=
got msg: 12
send msg: >=
got msg: 14
send msg: <
got msg: 13
send msg: <
got msg: ! 12
The final answer is: 12
Answer was correct!