按位与+掩码判断 | HJ39 判断两个IP是否属于同一子网

# 最优解
while 1:
    try:
        mask = list(map(int, input().split('.')))
        ip1 = list(map(int, input().split('.')))
        ip2 = list(map(int, input().split('.')))
        f = True
        for i in range(len(mask)):
            if mask[i] not in range(256) or ip1[i] not in range(256) or ip2[i] not in range(256):
                f = False
                break
            if i<len(mask)-1 and mask[i] < mask[i+1]:
                f = False
                break
        t1,t2= [],[]
        if f:
            for i in range(len(mask)):
                t1.append(mask[i]&ip1[i])
                t2.append(mask[i]&ip2[i])
            if t1==t2:
                print(0)
            else: print(2)
        else: print(1)       
    except:break

# 我的代码
def is_ip_valid(ip):
    for seg in ip:
        if int(seg) < 0 or int(seg) > 255:
            return False
    return True

def is_mask_valid(mask):
    if not is_ip_valid(mask):
        return False
    bin_mask = ''
    for seg in mask:
        bin_seg = '{:0>8}'.format(bin(int(seg))[2:])
        bin_mask += bin_seg
    for i in range(1, 33):
        tmp = bin_mask[i:]
        if bin_mask[i]=='0':
            return int(tmp) == 0

def mask_ip(ip, maks):
    res = []
    for ip_seg, mask_seg in zip(ip, mask):
        res.append(str(int(ip_seg) & int(mask_seg)))
    return '.'.join(res)

while True:
    try:
        mask = input().split('.')
        ip1 = input().split('.')
        ip2 = input().split('.')
        if not is_ip_valid(ip1) or not is_ip_valid(ip2) or not is_mask_valid(mask):
            print(1)
        else:
            res1 = mask_ip(ip1, mask)
            res2 = mask_ip(ip2, mask)
            if res1 == res2:
                print(0)
            else:
                print(2)
    except:
        break

要点：

1、两个ip同属子网判断：int数值按位与&

2、子网掩码合法判断：出现后项大于前项为非法（二进制，不是十进制）；寻找二进制掩码最后一个“1”和首个“0”索引之差，为1合法