Python | C++ | Remove leading zeros from an IP address

Given an IP address, remove leading zeros from the IP address.

Examples:

Input : 100.020.003.400 
Output : 100.20.3.400

Input :001.200.001.004  
Output : 1.200.1.4

The approach is to split the given string by “.” and then convert it to an integer which removes the leading zeros and then join back them to a string.To convert a string to an integer we can use int(s) and then convert it back to string by str(s) and then join them back by using join function.

Implementation:

C++

// Cpp program to remove leading zeros
// an IP address and print the IP

#include <bits/stdc++.h>
using namespace std;

// function to remove leading zeros
string removeZeros(string s)
{
    vector<string> v;

    // splits the ip by "."
    for (int i = 0; i < s.length(); i++) {
        string ans;
        while (i < s.length() && s[i] != '.') {
            ans += s[i];
            i++;
        }
        v.push_back(ans);
    }

    vector<int> num;
    // converts the words to integers to remove leading removeZeros
    for (auto str : v) {
        int temp = 0;
        for (int i = 0; i < str.length(); i++) {
            temp *= 10;
            temp += (str[i] - '0');
        }
        num.push_back(temp);
    }

    string ans = "";
    // Convert back the integer to string and join them back to a string
    for (auto i : num) {
        ans += '.';
        string temp;
        while (i) {
            temp += ('0' + (i % 10));
            i /= 10;
        }
        reverse(temp.begin(), temp.end());
        ans += temp;
    }

    return ans.substr(1);
}

int main()
{
    string ip;
    // example1
    ip = "100.020.003.400";
    cout << (removeZeros(ip)) << "\n";
    // example2
    ip = "001.200.001.004";
    cout << (removeZeros(ip)) << "\n";
    return 0;
}

Python

# Python program to remove leading zeros
# an IP address and print the IP

# function to remove leading zeros
def removeZeros(ip):

    # splits the ip by "."
    # converts the words to integers to remove leading removeZeros
    # convert back the integer to string and join them back to a string
    new_ip = ".".join([str(int(i)) for i in ip.split(".")])
    return new_ip ;


# driver code
# example1
ip ="100.020.003.400"
print(removeZeros(ip))


# example2
ip ="001.200.001.004"
print(removeZeros(ip))

Output

100.20.3.400
1.200.1.4

Method 2 : Regex

Using a capture group, match the last digit and copy it and prevents all the digits from being replaced. 
regex \d can be explained as: 

• \d : Matches any decimal digit

\d   Matches any decimal digit, this is equivalent
     to the set class [0-9].

• \b allows you to perform a “whole words only” search using a regular expression in the form of \bword\b 
  regex \b can be explained as:

\b allows you to perform a "whole words only" search u
sing a regular expression in the form of \bword\b

Implementation:

Python

# Python program to remove leading zeros
# an IP address and print the IP using regex
import re

# function to remove leading zeros
def removeZeros(ip):
    new_ip = re.sub(r'\b0+(\d)', r'\1', ip)
    # splits the ip by "."
    # converts the words to integers to remove leading removeZeros
    # convert back the integer to string and join them back to a string

    return new_ip


# driver code
# example1
ip ="100.020.003.400"
print(removeZeros(ip))


# example2
ip ="001.200.001.004"
print(removeZeros(ip))

Output

100.20.3.400
1.200.1.4

Method 3: Storing the index of the first non zero character.

The approach is to split the string by “.” and store it in another string x.

Now get the index of the first non-zero character of that string and store

it in another variable ind. Initialise that variable to -1 which indicates that there is

no non-zero character in the string .In another variable append the substring picking

up characters from that index till the end in another string y.

Source code : c++ solution

C++

#include<bits/stdc++.h>
using namespace std;
int main()
{
   string s="152.02.0015.00";
   string newIPAdd(string);
   cout<<newIPAdd(s);
   return 0;
}
string newIPAdd (string s)
   {
       long long int i,l,f=0,ind=-1;// initialising ind to -1 to indicate that there is no non-zero character in the string
       string x="",y="";
       char c;
       s=s+".";
       l=s.length();
       for(i=0;i<l;i++)
       {
           c=s.at(i);
           if(c!='.')
           {
               x=x+c;
               if(c!='0' && f==0)
               {
                   ind=x.length()-1;// getting the index of first non-zero character
                   f=1;//flag=1 to prevent further change of index for another non-zero character
               }

           }
           else
           {

               if(ind==-1)
               y=y+"."+"0";
               else
               y=y+"."+x.substr(ind);//appending it to the another string
               ind=-1;f=0;x="";
           }
       }
       return y.substr(1);
   }

Output

152.2.15.0