leetCode/ipValidator.java at master · abhisheksinghanand/leetCode · GitHub

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class Solution {
    public String validIPAddress(String IP) {
        if (IP == null || IP.length() == 0) {
            return "Neither";
        }

        if (IP.contains(".")) {
            boolean valid = validateIPv4(IP);
            if (valid) {
                return "IPv4";
            }
        } else if (IP.contains(":")) {
            boolean valid = validateIPv6(IP);
            if (valid) {
                return "IPv6";
            }
        }

        return "Neither";
    }

    private boolean validateIPv4(String s) {
        String[] tokens = s.split("[.]");
        if (tokens.length != 4) {
            return false;
        }

        if (s.charAt(0) == '.' || s.charAt(s.length() - 1) == '.') {
            return false;
        }

        for (String token : tokens) {
            if (!validateIpv4Helper(token)) {
                return false;
            }
        }

        return true;
    }

    private boolean validateIpv4Helper(String s) {
        if (s == null || s.length() == 0 || s.length() > 3) {
            return false;
        }

        if (s.length() > 1 && s.charAt(0) == '0') {
            return false;
        }

        int num = 0;
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c < '0' || c > '9') {
                return false;
            }

            int digit = (int)(c - '0');
            num = num * 10 + digit;
        }

        if (num < 0 || num > 255) {
            return false;
        }

        return true;
    }

    private boolean validateIPv6(String s) {
        if (s.charAt(0) == ':' || s.charAt(s.length() - 1) == ':') {
            return false;
        }

        String[] tokens = s.split("[:]");
        if (tokens.length != 8) {
            return false;
        }

        for (String token : tokens) {
            if (!validateIpv6Helper(token)) {
                return false;
            }
        }

        return true;
    }

    private boolean validateIpv6Helper(String s) {
        if (s == null || s.length() == 0 || s.length() > 4) {
            return false;
        }

        s = s.toLowerCase();

        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (Character.isDigit(c)) {
                if (c < '0' || c > '9') {
                    return false;
                }
            } else {
                if (c < 'a' || c > 'f') {
                    return false;
                }
            }
        }

        return true;
    }
}