Convert the number from International system to Indian system

Given string str which represents a number with separators(, ) in the International number system, the task is to convert this string representation into the Indian Numeric System. 
Examples:

Input: str = “123, 456, 789” 
Output: 12, 34, 56, 789 
Explanation:
The given string represents a number in the international system. It is converted to the Indian system. 
Input: str = “90, 050, 000, 000” 
Output: 90, 05, 00, 00, 000 

International Numeric System: The International numbering system is used outside the Indian subcontinent to express large numbers. It follows the following schema:

Number	Applying separators	In words
1	1	One
10	10	Ten
100	100	One hundred
1000	1, 000	One thousand
10000	10, 000	Ten thousand
100000	100, 000	One hundred thousand
1000000	1, 000, 000	One million
10000000	10, 000, 000	Ten million
100000000	100, 000, 000	One hundred million
1000000000	1, 000, 000, 000	One billion

Indian Numeric System: The Indian numbering system is used in the Indian subcontinent to express large numbers. It follows the following schema:

Number	Applying separators	In words
1	1	One
10	10	Ten
100	100	One hundred
1000	1, 000	One thousand
10000	10, 000	Ten thousand
100000	1, 00, 000	One lakh
1000000	10, 00, 000	Ten lakh
10000000	1, 00, 00, 000	One crore
100000000	10, 00, 00, 000	Ten crore
1000000000	100, 00, 00, 000	One hundred crore

Approach: From the above representations, the idea is to first obtain the number without any separators. Therefore: 

1. Remove all the separators(, ) from the string.
2. Reverse the string.
3. Process the string and put a separator(, ) after the third number.
4. Now put a separator(, ) after every second number. This converts the number into the Indian Numeric System.
5. Reverse the string again and print it.

Below is the implementation of the above approach:

C++

// C++ program to convert the number
// from International system
// to Indian system

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

// Function to convert a number represented
// in International numeric system to
// Indian numeric system.
string convert(string input)
{
    // Find the length of the
    // input string
    int len = input.length();

    // Removing all the separators(, )
    // from the input string
    for (int i = 0; i < len;) {

        if (input[i] == ', ') {
            input.erase(input.begin() + i);
            len--;
            i--;
        }
        else if (input[i] == ' ') {
            input.erase(input.begin() + i);
            len--;
            i--;
        }
        else {
            i++;
        }
    }

    // Reverse the input string
    reverse(input.begin(), input.end());

    // Declaring the output string
    string output;

    // Process the input string
    for (int i = 0; i < len; i++) {
        // Add a separator(, ) after the
        // third number
        if (i == 2) {
            output += input[i];
            output += ", ";
        }

        // Then add a separator(, ) after
        // every second number
        else if (i > 2 && i % 2 == 0
                 && i + 1 < len) {
            output += input[i];
            output += ", ";
        }
        else {
            output += input[i];
        }
    }

    // Reverse the output string
    reverse(output.begin(), output.end());

    // Return the output string back
    // to the main function
    return output;
}

// Driver code
int main()
{
    string input1 = "123, 456, 789";
    string input2 = "90, 050, 000, 000";

    cout << convert(input1) << endl;
    cout << convert(input2);
}

Java

// Java program to convert the number
// from International system
// to Indian system
import java.util.*;
class GFG{

// Function to convert a number represented
// in International numeric system to
// Indian numeric system.
static String convert(String input)
{
    StringBuilder sbInput = new StringBuilder(input);

    // Find the length of the
    // sbInput
    int len = sbInput.length();

    // Removing all the separators(, )
    // from the sbInput
    for (int i = 0; i < len;)
    {
        if (sbInput.charAt(i) == ',')
        {
            sbInput.deleteCharAt(i);
            len--;
            i--;
        }
        else if (sbInput.charAt(i) == ' ')
        {
            sbInput.deleteCharAt(i);
            len--;
            i--;
        }
        else
        {
            i++;
        }
    }

    // Reverse the sbInput
    StringBuilder sbInputReverse = sbInput.reverse();

    // Declaring the output
    StringBuilder output = new StringBuilder();

    // Process the sbInput
    for (int i = 0; i < len; i++)
    {

        // Add a separator(, ) after the
        // third number
        if (i == 2)
        {
            output.append(sbInputReverse.charAt(i));
            output.append(" ,");
        }

        // Then add a separator(, ) after
        // every second number
        else if (i > 2 && i % 2 == 0 && i + 1 < len)
        {
            output.append(sbInputReverse.charAt(i));
            output.append(" ,");
        }
        else
        {
            output.append(sbInputReverse.charAt(i));
        }
    }

    // Reverse the output
    StringBuilder reverseOutput = output.reverse();

    // Return the output string back
    // to the main function
    return reverseOutput.toString();
}

// Driver code
public static void main(String[] args)
{
    String input1 = "123, 456, 789";
    String input2 = "90, 050, 000, 000";

    System.out.println(convert(input1));
    System.out.println(convert(input2));
}
}

// This code is contributed by offbeat

Python3

# Python3 program to convert
# the number from International
# system to Indian system

# Function to convert a number
# represented in International
# numeric system to Indian numeric
# system.
def convert(input):

    # Find the length of the
    # input string
    Len = len(input)

    # Removing all the separators(, )
    # from the input string
    i = 0
    while(i < Len):
        if(input[i] == ","):
            input = input[:i] + input[i + 1:]
            Len -= 1
            i -= 1
        elif(input[i] == " "):
            input=input[:i] + input[i + 1:]
            Len -= 1
            i -= 1
        else:
            i += 1
    # Reverse the input string
    input=input[::-1]

    # Declaring the output string
    output = ""

    # Process the input string
    for i in range(Len):

        # Add a separator(, ) after the
        # third number
        if(i == 2):
            output += input[i]
            output += " ,"

        # Then add a separator(, ) after
        # every second number
        elif(i > 2 and i % 2 == 0 and
             i + 1 < Len):
            output += input[i]
            output += " ,"
        else:
            output += input[i]

    # Reverse the output string
    output=output[::-1]

    # Return the output string back
    # to the main function
    return output

# Driver code
input1 = "123, 456, 789"
input2 = "90, 050, 000, 000"
print(convert(input1))
print(convert(input2))

# This code is contributed by avanitrachhadiya2155

C#

// C# program to convert the number
// from International system
// to Indian system
using System;
using System.Linq;
using System.Text;
using System.Collections.Generic;

class GFG {

  // Function to convert a number represented
  // in International numeric system to
  // Indian numeric system.
  static string convert(string input)
  {
    StringBuilder sbInput = new StringBuilder(input);

    // Find the length of the
    // sbInput
    int len = sbInput.Length;

    // Removing all the separators(, )
    // from the sbInput
    for (int i = 0; i < len;) {
      if (sbInput[i] == ',') {
        sbInput.Remove(i, 1);
        len--;
        i--;
      }
      else if (sbInput[i] == ' ') {
        sbInput.Remove(i, 1);
        len--;
        i--;
      }
      else {
        i++;
      }
    }

    // Reverse the sbInput
    StringBuilder sbInputReverse = new StringBuilder();

    string st1 = new string(
      sbInput.ToString().Reverse().ToArray());
    sbInputReverse.Append(st1);

    // Declaring the output
    StringBuilder output = new StringBuilder();

    // Process the sbInput
    for (int i = 0; i < len; i++) {

      // Add a separator(, ) after the
      // third number
      if (i == 2) {
        output.Append(sbInputReverse[i]);
        output.Append(" ,");
      }

      // Then add a separator(, ) after
      // every second number
      else if (i > 2 && i % 2 == 0 && i + 1 < len) {
        output.Append(sbInputReverse[i]);
        output.Append(" ,");
      }
      else {
        output.Append(sbInputReverse[i]);
      }
    }

    // Reverse the output
    StringBuilder reverseOutput = new StringBuilder();

    st1 = new string(
      output.ToString().Reverse().ToArray());
    reverseOutput.Append(st1);

    // Return the output string back
    // to the main function
    return reverseOutput.ToString();
  }

  // Driver code
  public static void Main(string[] args)
  {
    string input1 = "123, 456, 789";
    string input2 = "90, 050, 000, 000";

    Console.WriteLine(convert(input1));
    Console.WriteLine(convert(input2));
  }
}

// This code is contributed by phasing17

Javascript

<script>

// JavaScript program to convert the number
// from International system
// to Indian system

// Function to convert a number represented
// in International numeric system to
// Indian numeric system.
function convert(input)
{
    // Find the length of the
    // input string
    let len = input.length;

    // Removing all the separators(, )
    // from the input string
    for (let i = 0; i < len;) {

        if (input[i] == ',') {
            input = input.substring(0,i) + input.substring(i+1,);
            len--;
            i--;
        }
        else if (input[i] == ' ') {
            input = input.substring(0,i) + input.substring(i+1,);
            len--;
            i--;
        }
        else {
            i++;
        }
    }

    // Reverse the input string
    input = input.split("").reverse().join("");

    // Declaring the output string
    let output = "";

    // Process the input string
    for (let i = 0; i < len; i++) {
        // Add a separator(, ) after the
        // third number
        if (i == 2) {
            output += input[i];
            output += " ,";
        }

        // Then add a separator(, ) after
        // every second number
        else if (i > 2 && i % 2 == 0
                 && i + 1 < len) {
            output += input[i];
            output += " ,";
        }
        else {
            output += input[i];
        }
    }

    // Reverse the output string
    output = output.split("").reverse().join("");

    // Return the output string back
    // to the main function
    return output;
}

// Driver code

let input1 = "123, 456, 789";
let input2 = "90, 050, 000, 000";

document.write(convert(input1),"</br>");
document.write(convert(input2),"</br>");

// This code is contributed by shinjanpatra

</script>

Output:

12, 34, 56, 789
90, 05, 00, 00, 000

Time Complexity: O(n²)

Auxiliary Space: O(1)