Code in C++ (Visit www.youtube.com/c/faadcoder for Explanation)

 #include<bits/stdc++.h>

using namespace std;

#define ll long long int

bool isValidIP(string &str)

{

if(str.length()>3)

return false;

if(str.front()=='0' and str.length()>1)

return false;

ll val=stoll(str);

return val>=0 and val<=255;

}

void computeAllValidIPAdress(string &str,vector<string> &res)

{

for(ll i=1;i<=3 and i<str.length();i++)

{

string first=str.substr(0,i);

if(isValidIP(first))

{

for(ll j=1;j<=3 and i+j<str.length();j++)

{

string second=str.substr(i,j);

if(isValidIP(second))

{

for(ll k=1;k<=3 and i+j+k<str.length();k++)

{

string third=str.substr(i+j,k);

string fourth=str.substr(i+j+k);

if(isValidIP(third) and isValidIP(fourth))

{

res.emplace_back(first+"."+second+"."+third+"."+fourth);

}

}

}

}

}

}

}

int main()

{

string str;

cin>>str;

vector<string> res;

        computeAllValidIPAdress(str,res);

        for(auto i:res)

cout<<i<<"\n";

        return 0;

}