給一個字串 IP ，回傳其屬於 IPv4 或 IPv6 或都不是 Neighter。
如果要找「合格」的字串，會想到用 re 去解決，這是在一般的情況下。如果是LeetCode，也許就不會用它。
不過官方的解法是有用到 re 的，直接傻眼，但那確實是最正當的解法。
通過「正則表達式(Regex)」是最嚴謹的做法，但也要有支持這項功能，在未知跟沒有的情況下，只能土炮出來。
這裡要從根本講，不論IPv6或是IPv4對電腦來說都是連續的二進位，IPv4長度為32bit，IPv6為128bit。
給人看的十進位跟十六進位是經由轉換而來的，如果換回原來的二進位形式，就只要留意是否長度是否合格就好。
所以把 string IP 轉換成連續二進位，就能輕而易舉去找出是否為合格的IP位置。(但是寫轉換的過程不容易)
在 IPv4 中用「.」做分隔，是用十進位的數字，分四段，每一段要有8bit。
在 IPv6 中用「:」做分隔，是用十六進位的數字，分八段，每一段要有32bit。
寫成IP轉換版，轉 IPv6 或 IPv4 的流程是大同小異的，甚至可以只用一個函數修改一些傳入參數就能變成IPv4或IPv6皆可的式子。
Python
class Solution:
def validIPAddress(self, IP: str) -> str:
deci = {*"0123456789"}
hexdeci = {*"0123456789abcdef"}
def checkIPv4(IP):
group = IP.split(".")
if len(group) != 4: return False
for seg in group:
if not(3 >= len(seg) >= 1): return False
if any([c not in deci for c in seg]): return False
if not(255 >= int(seg) >= 0): return False
if str(int(seg)) != seg: return False
return True
def checkIPv6(IP):
group = IP.lower().split(":")
if len(group) != 8: return False
for seg in group:
if not(4 >= len(seg) >= 1): return False
if any([c not in hexdeci for c in seg]): return False
return True
if checkIPv4(IP): return "IPv4"
if checkIPv6(IP): return "IPv6"
return "Neither"
Python(IP轉換版)
class Solution:
def validIPAddress(self, IP: str) -> str:
decimal = {*"0123456789"}
def covertIPv4(IP):
IPv4 = ""
seg = ""
segCount = 0
for c in IP:
if c == ".":
segCount += 1
if segCount >= 4 or not seg: return False
if len(seg) > 1 and seg[0] == '0': return False
seg = "{:0>8}".format(bin(int(seg))[2:])
if len(seg) > 8: return False
IPv4 += seg
seg = ""
elif c in decimal:
seg += c
else:
return False
if seg:
if len(seg) > 1 and seg[0] == '0': return False
seg = "{:0>8}".format(bin(int(seg))[2:])
if len(seg) > 8: return False
IPv4 += seg
return len(IPv4) == 32
hexadecimal = {*"0123456789abcdefABCDEF"}
def covertIPv6(IP):
IPv6 = ""
seg = ""
segCount = 0
for c in IP:
if c == ":":
segCount += 1
if segCount >= 8 or not seg: return False
seg = "{:0>16}".format(seg)
if len(seg) > 16: return False
IPv6 += seg
seg = ""
elif c in hexadecimal:
seg += "{:0>4}".format(bin(int(c, 16))[2:])
else:
return False
if seg:
seg = "{:0>16}".format(seg)
if len(seg) > 16: return False
IPv6 += seg
return len(IPv6) == 128
if covertIPv4(IP): return "IPv4"
if covertIPv6(IP): return "IPv6"
return "Neither"
Python(IP轉換合一版)
class Solution:
def validIPAddress(self, IP: str) -> str:
decimal = {*"0123456789"}
hexadecimal = {*"0123456789abcdef"}
def covertIP(strIP, Segs, PerSegBit, Carry, Delimiter):
def addSeg(IP, seg):
if segCount >= Segs or not seg: return False
if Delimiter == "." and len(seg) > 1 and seg[0] == '0': return False
if Delimiter == ":" and len(seg) > 4: return False
try:
seg = ("{:0>"+str(PerSegBit)+"}").format(bin(int(seg, len(Carry)))[2:])
except:
return False
if len(seg) > PerSegBit: return False
return IP + seg
IP = seg = ""
segCount = 0
for c in strIP.lower():
if c == Delimiter:
segCount += 1
IP = addSeg(IP, seg)
if not IP: return False
seg = ""
elif c in Carry:
seg += c
else:
return False
if not seg: return False
IP = addSeg(IP, seg)
if not IP: return False
return len(IP) == Segs * PerSegBit
if covertIP(IP, 4, 8, decimal, "."): return "IPv4"
if covertIP(IP, 8, 16, hexadecimal, ":"): return "IPv6"
return "Neither"
C#
public class Solution {
public string ValidIPAddress(string IP) {
if(IsIPv4(IP)){return "IPv4";}
if(IsIPv6(IP)){return "IPv6";}
return "Neither";
}
private bool IsIPv4(string IP) {
var parts = IP.Split('.');
if(parts.Length != 4){return false;}
int dec = 0;
foreach(var part in parts)
{
if(!(Int32.TryParse(part, out dec))){return false;}
if(dec 255 || (dec.ToString().Length != part.Length)){return false;}
}
return true;
}
private bool IsIPv6(string IP) {
var parts = IP.Split(':');
if(parts.Length != 8){return false;}
int hex;
foreach(var part in parts)
{
if(part.Length > 4){return false;}
if(!Int32.TryParse(part,
System.Globalization.NumberStyles.HexNumber,
null,
out hex)){return false;}
if(hex < 0){return false;}
}
return true;
}
}
TestCase
"1.1.1.01"
"01.01.01.01"
"001.001.001.001"
"301.301.301.301"
"12..33.4"
"1.0.1."
"1.-1.1.1"
"0.0.0.0"
"172.16.254.1"
"256.256.256.256"
"2001:0db8:85a3:0:0:8A2E:0370:7334"
"2001:0db8:85a3::8A2E:0370:7334"
"2001:db8:85a3:0:0:8A2E:0370:7334"
"20EE:FGb8:85a3:0:0:8A2E:0370:7334"
"2001:0db8:85a3:00000:0:8A2E:0370:7334"
"1081:db8:85a3:01:-0:8A2E:0370:7334"
"2001:0db8:85a3:0:0:8A2E:0370:7334:"