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方法二：分治法

思想

IPv4 和 IPv6 地址均是由特定的分界符隔开的字符串组成，并且每个子字符串具有相同格式。

因此，可以将地址分为多个块，然后逐块进行验证。

仅当每个块都有效时，该地址才有效。这种方法称为分治法。

算法

• 对于 IPv4 地址，通过界定符 . 将地址分为四块；对于 IPv6 地址，通过界定符 : 将地址分为八块。
• 对于 IPv4 地址的每一块，检查它们是否在 0 - 255 内，且没有前置零。
• 对于 IPv6 地址的每一块，检查其长度是否为 1 - 4 位的十六进制数。

Python 实现

class Solution: def validate_IPv4(self, IP: str) -> str: nums = IP.split('.') for x in nums: # Validate integer in range (0, 255): # 1. length of chunk is between 1 and 3 if len(x) == 0 or len(x) > 3: return "Neither" # 2. no extra leading zeros # 3. only digits are allowed # 4. less than 255 if x[0] == '0' and len(x) != 1 or not x.isdigit() or int(x) > 255: return "Neither" return "IPv4" def validate_IPv6(self, IP: str) -> str: nums = IP.split(':') hexdigits = '0123456789abcdefABCDEF' for x in nums: # Validate hexadecimal in range (0, 2**16): # 1. at least one and not more than 4 hexdigits in one chunk # 2. only hexdigits are allowed: 0-9, a-f, A-F if len(x) == 0 or len(x) > 4 or not all(c in hexdigits for c in x): return "Neither" return "IPv6" def validIPAddress(self, IP: str) -> str: if IP.count('.') == 3: return self.validate_IPv4(IP) elif IP.count(':') == 7: return self.validate_IPv6(IP) else: return "Neither"

Java 实现

class Solution { public String validateIPv4(String IP) { String[] nums = IP.split("\\.", -1); for (String x : nums) { // Validate integer in range (0, 255): // 1. length of chunk is between 1 and 3 if (x.length() == 0 || x.length() > 3) return "Neither"; // 2. no extra leading zeros if (x.charAt(0) == '0' && x.length() != 1) return "Neither"; // 3. only digits are allowed for (char ch : x.toCharArray()) { if (! Character.isDigit(ch)) return "Neither"; } // 4. less than 255 if (Integer.parseInt(x) > 255) return "Neither"; } return "IPv4"; } public String validateIPv6(String IP) { String[] nums = IP.split(":", -1); String hexdigits = "0123456789abcdefABCDEF"; for (String x : nums) { // Validate hexadecimal in range (0, 2**16): // 1. at least one and not more than 4 hexdigits in one chunk if (x.length() == 0 || x.length() > 4) return "Neither"; // 2. only hexdigits are allowed: 0-9, a-f, A-F for (Character ch : x.toCharArray()) { if (hexdigits.indexOf(ch) == -1) return "Neither"; } } return "IPv6"; } public String validIPAddress(String IP) { if (IP.chars().filter(ch -> ch == '.').count() == 3) { return validateIPv4(IP); } else if (IP.chars().filter(ch -> ch == ':').count() == 7) { return validateIPv6(IP); } else return "Neither"; } }

复杂度分析