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# 0468. Validate IP Address

<https://leetcode.com/problems/validate-ip-address>

## Description

Given a string `IP`, return `"IPv4"` if IP is a valid IPv4 address, `"IPv6"` if IP is a valid IPv6 address or `"Neither"` if IP is not a correct IP of any type.

**A valid IPv4** address is an IP in the form `"x1.x2.x3.x4"` where `0 <= xi <= 255` and `xi` **cannot contain** leading zeros. For example, `"192.168.1.1"` and `"192.168.1.0"` are valid IPv4 addresses but `"192.168.01.1"`, while `"192.168.1.00"` and `"192.168@1.1"` are invalid IPv4 addresses.

**A valid IPv6** address is an IP in the form `"x1:x2:x3:x4:x5:x6:x7:x8"` where:

* `1 <= xi.length <= 4`
* `xi` is a **hexadecimal string** which may contain digits, lower-case English letter (`'a'` to `'f'`) and upper-case English letters (`'A'` to `'F'`).
* Leading zeros are allowed in `xi`.

For example, "`2001:0db8:85a3:0000:0000:8a2e:0370:7334"` and "`2001:db8:85a3:0:0:8A2E:0370:7334"` are valid IPv6 addresses, while "`2001:0db8:85a3::8A2E:037j:7334"` and "`02001:0db8:85a3:0000:0000:8a2e:0370:7334"` are invalid IPv6 addresses.

**Example 1:**

```
**Input:** IP = "172.16.254.1"
**Output:** "IPv4"
**Explanation:** This is a valid IPv4 address, return "IPv4".
```

**Example 2:**

```
**Input:** IP = "2001:0db8:85a3:0:0:8A2E:0370:7334"
**Output:** "IPv6"
**Explanation:** This is a valid IPv6 address, return "IPv6".
```

**Example 3:**

```
**Input:** IP = "256.256.256.256"
**Output:** "Neither"
**Explanation:** This is neither a IPv4 address nor a IPv6 address.
```

**Example 4:**

```
**Input:** IP = "2001:0db8:85a3:0:0:8A2E:0370:7334:"
**Output:** "Neither"
```

**Example 5:**

```
**Input:** IP = "1e1.4.5.6"
**Output:** "Neither"
```

**Constraints:**

* `IP` consists only of English letters, digits and the characters `'.'` and `':'`.

## ac

```java
class Solution {
    public String validIPAddress(String IP) {
        int i4 = IP.indexOf(".");
        int i6 = IP.indexOf(":");
        if (i4 >= 0 && i6 < 0) {
            if (valid4(IP)) return "IPv4";
        } else if (i6 >= 0 && i4 < 0) {
            if (valid6(IP)) return "IPv6";
        }

        return "Neither";
    }

    public boolean valid4(String s) {
        String[] strs = s.split("\\.");
        if (strs.length != 4 || s.charAt(s.length()-1) == '.') return false;
        for (String str : strs) {
            if (str.length() == 0 || 
                str.length() > 1 && str.startsWith("0") || str.length() > 3) return false;
            for (char c : str.toCharArray()) {
                if (!Character.isDigit(c)) return false;
            }
            int val = Integer.parseInt(str);
            if (val < 0 || val > 255) return false;
        }
        return true;
    }

    public boolean valid6(String s) {
        String[] strs = s.split(":");
        if (strs.length != 8 || s.charAt(s.length()-1) == ':') return false;
        for (String str : strs) {
            if (str.length() == 0 || str.length() > 4) return false;
            for (char c : str.toUpperCase().toCharArray()) {
                if ((c < '0' || c > '9') && (c < 'A' || c > 'F')) return false;
            }
        }

        return true;
    }
}

/*
1) v4 only contains ., v6 only contains : 2) split by ./:, careful "\\."; 3) check String[] length, last char can't be seperator; 4) check each char length; 5) check char within range;
*/
```


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