题解 | #判断两个IP是否属于同一子网#

mask = input().strip().split(".")
ip1 = input().strip().split(".")
ip2 = input().strip().split(".")


def identify(mask: list[str], ip1: list[str], ip2: list[str]):
    if not identify_mask(mask) or not identify_ip(ip1) or not identify_ip(ip2):
        print(1)
        return

    for i in range(4):
        res1 = logic_and(mask[i], ip1[i])
        res2 = logic_and(mask[i], ip2[i])
        if res1 != res2:
            print(2)
            return
    
    print(0)



def identify_mask(mask: list[str]):
    if len(mask) != 4:
        return False

    if mask[0] == "0" or mask[3] == "255":
        return False

    for i in range(4):
        if not mask[i].isnumeric():
            return False

        if mask[i] == "0":
            if i < 3:
                if mask[i + 1] != "0":
                    return False
            continue

        temp = int(mask[i])


        if 0 < temp < 128 or (not 0 <= temp <= 255):
            return False

        # 判断二进制形式是否为连续的1
        for j in range(7, -1, -1):
            temp -= 2 ** j
            if temp < 0:
                return False
            elif temp == 0:
                if i != 3 and j > 0:
                    # 不是255但是是其他二进制是连续的1的数，那么mask中剩余的数必须都是0才是合法的mask
                    if mask[i + 1 :].count("0") != 4 - i - 1:
                        return False
                break
    return True

def identify_ip(ip: list[str]):
    if len(ip) != 4:
        return False

    for i in ip:
        if not i.isnumeric():
            return False
        
        temp = int(i)
        
        if not 0 <= temp <= 255:
            return False

    return True

def logic_and(mask: str, ip: str):
    ma = bin(int(mask))[2:]
    pi = bin(int(ip))[2:]

    if len(ma) < 8:
        ma = '0' * (8-len(ma)) + ma
    
    if len(pi) < 8:
        pi = '0' * (8-len(pi)) + pi

    o = []

    for i in range(8):
        t1 = ma[i]
        t2 = pi[i]
        o.append(str(int(t1) & int(t2)))
    
    return ''.join(o)


identify(mask, ip1, ip2)