# Restore IP Addresses in C++

Suppose we have a string containing only digits, we have to restore it by returning all possible valid IP address combinations. We know that a valid IP address consists of exactly four integers (each integer is in range 0 to 255) separated by single points.

So, if the input is like "25525511135", then the output will be ["255.255.11.135", "255.255.111.35"]

To solve this, we will follow these steps −

• Define a function convertToNum(), this will take s, start, end,

• num := 0

• for initialize i := start, when i <= end, update (increase i by 1), do −

• num := (num * 10) + (s[i] - ASCII of '0')

• if num > 255, then −

• return 10000

• return num

• Define a function addDots(), this will take positions,

• res := blank string

• x := 0, posIndex := 0

• for initialize i := 0, when i < size of positions, update (increase i by 1), do −

• num := positions[i]

• create one string str1

• temp := num as string

• res := res + temp

• if i < size of positions, then −

• res := res concatenate "."

• return res

• Define a function solve(), this will take s, one string array result, an array positions, dotCount, this is initialize it with 3, startIndex, this is initialize it with 0,

• if not dotCount is non-zero and ((size of s - 1) - startIndex + 1) 1, then −

• temp := convertToNum(s, startIndex, size of s)

• if temp >= 0 and temp <= 255, then−

• insert temp at the end of positions

• if size of res is same as size of s, then −

• insert res at the end of result

• return

• for initialize i := startIndex, when i < size of s, update (increase i by 1), do −

• temp := convertToNum(s, startIndex, i)

• if temp >= 0 and temp <= 255, then −

• insert temp at the end of positions

• solve(s, result, positions, dotCount - 1, i + 1)

• delete last element from positions

• Define one function genIp this will take a string s,

• Define an array result

• Define an array position

• solve(s, result, position)

• return result

• From the main method call genIp(A)

## Example

Let us see the following implementation to get better understanding −

Live Demo

#include <bits/stdc++.h>
using namespace std;
void print_vector(vector<auto> v){
cout << "[";
for(int i = 0; i<v.size(); i++){
cout << v[i] << ", ";
}
cout << "]"<<endl;
}
typedef long long int lli;
class Solution {
public:
lli convertToNum(string s,int start, int end){
lli num = 0;
for (int i = start; i <= end; i++) {
num = (num * 10) + (s[i] - '0');
if (num > 255)
return 10000;
}
return num;
}
string res = "";
int x = 0;
int posIndex = 0;
for (int i = 0; i < positions.size(); i++) {
int num = positions[i];
ostringstream str1;
str1 << num;
string temp = str1.str();
res += temp;
if (i < positions.size() - 1)
res += ".";
}
return res;
}
void solve(string s, vector <string> &result,vector <int> positions, int dotCount = 3, int startIndex = 0){
if (!dotCount && ((s.size() - 1) - startIndex + 1) >= 1) {
int temp = convertToNum(s, startIndex, s.size() - 1);
if (temp >= 0 && temp <= 255) {
positions.push_back(temp);
if (res.size() - 3 == s.size()) {
result.push_back(res);
}
}
return;
}
for (int i = startIndex; i < s.size(); i++) {
int temp = convertToNum(s, startIndex, i);
if (temp >= 0 && temp <= 255) {
positions.push_back(temp);
solve(s, result, positions, dotCount - 1, i + 1);
positions.pop_back();
}
}
}
vector<string> genIp(string s){
vector<string> result;
vector<int> position;
solve(s, result, position);
return result;
}
return genIp(A);
}};
main(){
Solution ob;
}

## Input

"25525511135"

## Output

[255.255.11.135, 255.255.111.35, ]

Updated on: 17-Nov-2020

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