# Program to generate all possible valid IP addresses from given string

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

A valid IP address must be in the form of A.B.C.D, where A, B, C, and D are numbers from 0-255. The numbers cannot be 0 prefixed unless they are 0.

Examples :

```Input : 25525511135
Output : [“255.255.11.135”, “255.255.111.35”]
Explanation:
These are the only valid possible
IP addresses.

Input : "25505011535"
Output : []
Explanation :
We cannot generate a valid IP
address with this string.
```

First, we will place 3 dots in the given string and then Try out all the possible combinations for the 3 dots.
Corner case for validity :

```For string "25011255255"

25.011.255.255 is not valid as 011 is not valid.
25.11.255.255 is not valid either as you are not
allowed to change the string.
250.11.255.255 is valid.```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach :
Split the string with ‘ . ‘ and then check for all corner cases. Before entering the loop, check the size of string. Generate all the possible combinations using looping through the string. If IP is found to be valid then return the IP address, else simply return empty list.

Below is the implementation of above approach :

## Java

 `// Java Program to generate all possible ` `// valid IP addresses from given string ` `import` `java.util.*; ` ` `  `class` `GFG { ` `     `  `    ``// Function to restore Ip Addresses ` `    ``public` `static` `ArrayList restoreIpAddresses(String A)  ` `    ``{ ` `        ``if` `(A.length() < ``3` `|| A.length() > ``12``) ` `            ``return` `new` `ArrayList<>(); ` `        ``return` `convert(A); ` `    ``} ` ` `  `    ``private` `static` `ArrayList convert(String s)  ` `    ``{ ` `        ``ArrayList l =  ` `                  ``new` `ArrayList<>(); ` `        ``int` `size = s.length(); ` ` `  `        ``String snew = s; ` ` `  `        ``for` `(``int` `i = ``1``; i < size - ``2``;  ` `                               ``i++) ` `        ``{ ` `            ``for` `(``int` `j = i + ``1``;  ` `                 ``j < size - ``1``; j++)  ` `            ``{ ` `                ``for` `(``int` `k = j + ``1``;  ` `                     ``k < size; k++)  ` `                ``{ ` `                    ``snew = snew.substring(``0``, k) + ` `                           ``"."` `+ snew.substring(k); ` `                    ``snew = snew.substring(``0``, j) +  ` `                           ``"."` `+ snew.substring(j); ` `                    ``snew = snew.substring(``0``, i) +  ` `                           ``"."` `+ snew.substring(i);  ` `                            `  `                    ``if` `(isValid(snew)) ` `                    ``{ ` `                        ``l.add(snew); ` `                    ``} ` `                    ``snew = s; ` `                ``} ` `            ``} ` `        ``} ` ` `  `        ``Collections.sort(l, ``new` `Comparator()  ` `        ``{ ` `            ``public` `int` `compare(String o1, String o2) ` `            ``{ ` `                ``String a1[] = o1.split(``"[.]"``); ` `                ``String a2[] = o2.split(``"[.]"``); ` ` `  `                ``int` `result = -``1``; ` `                ``for` `(``int` `i = ``0``; i < ``4` `&&  ` `                     ``result != ``0``; i++)  ` `                ``{ ` `                    ``result = a1[i].compareTo(a2[i]); ` `                ``} ` `                ``return` `result; ` `            ``} ` `        ``}); ` `        ``return` `l; ` ` `  `    ``} ` ` `  `    ``private` `static` `boolean` `isValid(String ip)  ` `    ``{ ` `        ``String a[] = ip.split(``"[.]"``); ` `        ``for` `(String s : a) { ` `            ``int` `i = Integer.parseInt(s); ` `            ``if` `(s.length() > ``3` `|| i < ``0` `|| i > ``255``)  ` `            ``{ ` `                ``return` `false``; ` `            ``} ` `            ``if` `(s.length() > ``1` `&& i == ``0``) ` `                ``return` `false``; ` `            ``if` `(s.length() > ``1` `&& i != ``0` `&& ` `                        ``s.charAt(``0``) == ``'0'``) ` `                ``return` `false``; ` `        ``} ` ` `  `        ``return` `true``; ` `    ``} ` ` `  `// Driver Code ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``System.out.println(restoreIpAddresses ` `              ``(``"25525511135"``).toString()); ` `} ` `} ` ` `  `// This code is contributed by Nidhi Hooda. `

## Python3

 `# Python code to check valid possible IP ` ` `  `# Function checks wheather IP digits ` `# are valid or not. ` `def` `is_valid(ip): ` ` `  `    ``# Spliting by "." ` `    ``ip ``=` `ip.split(``"."``) ` `     `  `    ``# Checking for the corner cases ` `    ``for` `i ``in` `ip: ` `        ``if` `len``(i) > ``3` `or` `int``(i) < ``0` `or` `int``(i) > ``255``: ` `            ``return` `False` `        ``if` `len``(i) > ``1` `and` `int``(i) ``=``=` `0``: ` `            ``return` `False` `        ``if` `len``(i) > ``1` `and` `int``(i) !``=` `0` `and` `i[``0``] ``=``=` `'0'``: ` `            ``return` `False` `    ``return` `True` ` `  `# Function converts string to IP address ` `def` `convert(s): ` `    ``sz ``=` `len``(s) ` ` `  `    ``# Check for string size ` `    ``if` `sz > ``12``: ` `        ``return` `[] ` `    ``snew ``=` `s ` `    ``l ``=` `[] ` `-` `    ``# Generating different combinations. ` `    ``for` `i ``in` `range``(``1``, sz ``-` `2``): ` `        ``for` `j ``in` `range``(i ``+` `1``, sz ``-` `1``): ` `            ``for` `k ``in` `range``(j ``+` `1``, sz): ` `                ``snew ``=` `snew[:k] ``+` `"."` `+` `snew[k:] ` `                ``snew ``=` `snew[:j] ``+` `"."` `+` `snew[j:] ` `                ``snew ``=` `snew[:i] ``+` `"."` `+` `snew[i:] ` `                 `  `                ``# Check for the validity of combination ` `                ``if` `is_valid(snew): ` `                    ``l.append(snew) ` `                ``snew ``=` `s ` `    ``return` `l  ` ` `  `# Driver code          ` `A ``=` `"25525511135"` `B ``=` `"25505011535"` `print``(convert(A)) ` `print``(convert(B)) `

Output :

```['255.255.11.135', '255.255.111.35']
```

My Personal Notes arrow_drop_up If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Improved By : nidhi hooda

Article Tags :
Practice Tags :

1

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.