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Program to generate all possible valid IP addresses from given string | Set 2
• Difficulty Level : Hard
• Last Updated : 15 Jul, 2019

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: str = “25525511135”
Output:
255.255.11.135
255.255.111.35

Input: str = “11111011111”
Output:
111.110.11.111
111.110.111.11

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

Approach: This problem can be solved using backtracking. In each call we have three options to create a single block of numbers of a valid ip address:

1. Either select only a single digit, add a dot and move onto selecting other blocks (further function calls).
2. Or select two digits at the same time, add a dot and move further.
3. Or select three consecutive digits and move for the next block.

At the end of the fourth block, if all the digits have been used and the address generated is a valid ip-address then add it to the results and then backtrack by removing the digits selected in the previous call.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``#include ``using` `namespace` `std;`` ` `// Function to get all the valid ip-addresses``void` `GetAllValidIpAddress(vector& result,``                          ``string givenString, ``int` `index,``                          ``int` `count, string ipAddress)``{`` ` `    ``// If index greater than givenString size``    ``// and we have four block``    ``if` `(givenString.size() == index && count == 4) {`` ` `        ``// Remove the last dot``        ``ipAddress.pop_back();`` ` `        ``// Add ip-address to the results``        ``result.push_back(ipAddress);``        ``return``;``    ``}`` ` `    ``// To add one index to ip-address``    ``if` `(givenString.size() < index + 1)``        ``return``;`` ` `    ``// Select one digit and call the``    ``// same function for other blocks``    ``ipAddress = ipAddress``                ``+ givenString.substr(index, 1) + ``'.'``;``    ``GetAllValidIpAddress(result, givenString, index + 1,``                         ``count + 1, ipAddress);`` ` `    ``// Backtrack to generate another poosible ip address``    ``// So we remove two index (one for the digit``    ``// and other for the dot) from the end``    ``ipAddress.erase(ipAddress.end() - 2, ipAddress.end());`` ` `    ``// Select two consecutive digits and call``    ``// the same function for other blocks``    ``if` `(givenString.size() < index + 2``        ``|| givenString[index] == ``'0'``)``        ``return``;``    ``ipAddress = ipAddress + givenString.substr(index, 2) + ``'.'``;``    ``GetAllValidIpAddress(result, givenString, index + 2,``                         ``count + 1, ipAddress);`` ` `    ``// Backtrack to generate another poosible ip address``    ``// So we remove three index from the end``    ``ipAddress.erase(ipAddress.end() - 3, ipAddress.end());`` ` `    ``// Select three consecutive digits and call``    ``// the same function for other blocks``    ``if` `(givenString.size() < index + 3``        ``|| stoi(givenString.substr(index, 3)) > 255)``        ``return``;``    ``ipAddress += givenString.substr(index, 3) + ``'.'``;``    ``GetAllValidIpAddress(result, givenString, index + 3,``                         ``count + 1, ipAddress);`` ` `    ``// Backtrack to generate another poosible ip address``    ``// So we remove four index from the end``    ``ipAddress.erase(ipAddress.end() - 4, ipAddress.end());``}`` ` `// Driver code``int` `main()``{``    ``string givenString = ``"25525511135"``;`` ` `    ``// Fill result vector with all valid ip-addresses``    ``vector result;``    ``GetAllValidIpAddress(result, givenString, 0, 0, ``""``);`` ` `    ``// Print all the generated ip-addresses``    ``for` `(``int` `i = 0; i < result.size(); i++) {``        ``cout << result[i] << ``"\n"``;``    ``}``}`

## Python3

 `# Python3 implementation of the approach `` ` `# Function to get all the valid ip-addresses ``def` `GetAllValidIpAddress(result, givenString,``                         ``index, count, ipAddress) :`` ` `    ``# If index greater than givenString size ``    ``# and we have four block ``    ``if` `(``len``(givenString) ``=``=` `index ``and` `count ``=``=` `4``) :`` ` `        ``# Remove the last dot ``        ``ipAddress.pop(); `` ` `        ``# Add ip-address to the results ``        ``result.append(ipAddress); ``        ``return``; `` ` `    ``# To add one index to ip-address ``    ``if` `(``len``(givenString) < index ``+` `1``) :``        ``return``; `` ` `    ``# Select one digit and call the ``    ``# same function for other blocks ``    ``ipAddress ``=` `(ipAddress ``+` `                 ``givenString[index : index ``+` `1``] ``+` `[``'.'``]); ``     ` `    ``GetAllValidIpAddress(result, givenString, index ``+` `1``,``                                 ``count ``+` `1``, ipAddress); `` ` `    ``# Backtrack to generate another poosible ip address ``    ``# So we remove two index (one for the digit ``    ``# and other for the dot) from the end ``    ``ipAddress ``=` `ipAddress[:``-``2``];`` ` `    ``# Select two consecutive digits and call ``    ``# the same function for other blocks ``    ``if` `(``len``(givenString) < index ``+` `2` `or` `            ``givenString[index] ``=``=` `'0'``) :``        ``return``; ``         ` `    ``ipAddress ``=` `ipAddress ``+` `givenString[index:index ``+` `2``] ``+` `[``'.'``]; ``    ``GetAllValidIpAddress(result, givenString, index ``+` `2``, ``                                  ``count ``+` `1``, ipAddress); `` ` `    ``# Backtrack to generate another poosible ip address ``    ``# So we remove three index from the end ``    ``ipAddress ``=` `ipAddress[:``-``3``]; `` ` `    ``# Select three consecutive digits and call ``    ``# the same function for other blocks ``    ``if` `(``len``(givenString)< index ``+` `3` `or` `        ``int``("".join(givenString[index:index ``+` `3``])) > ``255``) :``        ``return``; ``    ``ipAddress ``+``=` `givenString[index:index ``+` `3``] ``+` `[``'.'``]; ``    ``GetAllValidIpAddress(result, givenString, ``                         ``index ``+` `3``, count ``+` `1``, ipAddress); `` ` `    ``# Backtrack to generate another poosible ip address ``    ``# So we remove four index from the end ``    ``ipAddress ``=` `ipAddress[:``-``4``]; `` ` `# Driver code ``if` `__name__ ``=``=` `"__main__"` `: ``    ``givenString ``=` `list``(``"25525511135"``); `` ` `    ``# Fill result vector with all valid ip-addresses ``    ``result ``=` `[] ; ``    ``GetAllValidIpAddress(result, givenString, ``0``, ``0``, []); `` ` `    ``# Print all the generated ip-addresses ``    ``for` `i ``in` `range``(``len``(result)) :``        ``print``("".join(result[i])); ``         ` `# This code is contributed by Ankitrai01`
Output:
```255.255.11.135
255.255.111.35
```

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