Sort an alphanumeric string such that the positions of alphabets and numbers remain unchanged

Given an alphanumeric string str, the task is to sort the string in such a way that if a position is occupied by an alphabet it must be occupied by an alphabet after sorting and if occupied by a number it must be occupied by a number after sorting.
Examples:

Input: str = “geeks12for32geeks” 
Output: eeeef12ggk23korss
Input: str = “d4c3b2a1” 
Output: a1b2c3d4 

Approach: We will convert the string to a character array and then sort the character array c[]. After sorting the character array the numeric characters will occupy starting indices of the array and the alphabets will occupy the remaining part of the array. 
The numeric half will be sorted and the alphabet part will also be sorted. We will keep two indices one at the starting index of the alphabet part al_c and one at the starting index of numeric part nu_c, now we will check the original string and if a position was occupied by an alphabet then we will replace it with c[al_c] and increment al_c else we will replace it with c[nu_c] and increment nu_c.
Below is the implementation of the above approach: 

C++

// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;

// Function that returns the string s
// in sorted form such that the
// positions of alphabets and numeric
// digits remain unchanged
string sort(string s)
{
    char c[s.length() + 1];

    // String to character array
    strcpy(c, s.c_str());

    // Sort the array
    sort(c, c + s.length());

    // Count of alphabets and numbers
    int al_c = 0, nu_c = 0;

    // Get the index from where the
    // alphabets start
    while (c[al_c] < 97)
        al_c++;

    // Now replace the string with sorted string
    for (int i = 0; i < s.length(); i++) {

        // If the position was occupied by an
        // alphabet then replace it with alphabet
        if (s[i] < 97)
            s[i] = c[nu_c++];

        // Else replace it with a number
        else
            s[i] = c[al_c++];
    }

    // Return the sorted string
    return s;
}

// Driver code
int main()
{
    string s = "d4c3b2a1";

    cout << sort(s);

    return 0;
}

Java

// A Java implementation of the approach
import java.util.*;

class GFG
{

// Function that returns the string s
// in sorted form such that the
// positions of alphabets and numeric
// digits remain unchanged
static String sort(String s)
{
    char []c = new char[s.length() + 1];

    // String to character array
    c = s.toCharArray();

    // Sort the array
    Arrays.sort(c);

    // Count of alphabets and numbers
    int al_c = 0, nu_c = 0;

    // Get the index from where the
    // alphabets start
    while (c[al_c] < 97)
        al_c++;

    // Now replace the string with sorted string
    for (int i = 0; i < s.length(); i++)
    {

        // If the position was occupied by an
        // alphabet then replace it with alphabet
        if (s.charAt(i) < 97)
            s = s.substring(0,i)+ c[nu_c++]+s.substring(i+1);

        // Else replace it with a number
        else
            s = s.substring(0,i)+ c[al_c++]+s.substring(i+1);
    }

    // Return the sorted string
    return s;
}

// Driver code
public static void main(String[] args)
{
    String s = "d4c3b2a1";

    System.out.println(sort(s));
}
}

/* This code contributed by PrinciRaj1992 */

Python3

# Python3 implementation of the approach

# Function that returns the string s
# in sorted form such that the
# positions of alphabets and numeric
# digits remain unchanged
def sort(s):

    # String to character array
    c, s = list(s), list(s)

    # Sort the array
    c.sort()

    # Count of alphabets and numbers
    al_c = 0
    nu_c = 0

    # Get the index from where the
    # alphabets start
    while ord(c[al_c]) < 97:
        al_c += 1

    # Now replace the string with sorted string
    for i in range(len(s)):

        # If the position was occupied by an
        # alphabet then replace it with alphabet
        if s[i] < 'a':
            s[i] = c[nu_c]
            nu_c += 1

        # Else replace it with a number
        else:
            s[i] = c[al_c]
            al_c += 1

    # Return the sorted string
    return ''.join(s)

# Driver Code
if __name__ == "__main__":
    s = "d4c3b2a1"
    print(sort(s))

# This code is contributed by
# sanjeev2552

C#

// C# implementation of the approach
using System;

class GFG
{

    // Function that returns the string s
    // in sorted form such that the
    // positions of alphabets and numeric
    // digits remain unchanged
    static string sort(string s)
    {
        char []c = new char[s.Length + 1];

        // String to character array
        c = s.ToCharArray();

        // Sort the array
        Array.Sort(c);

        // Count of alphabets and numbers
        int al_c = 0, nu_c = 0;

        // Get the index from where the
        // alphabets start
        while (c[al_c] < 97)
            al_c++;

        // Now replace the string with sorted string
        for (int i = 0; i < s.Length; i++)
        {

            // If the position was occupied by an
            // alphabet then replace it with alphabet
            if (s[i] < 97)
                s = s.Substring(0,i)+ c[nu_c++]+s.Substring(i+1);

            // Else replace it with a number
            else
                s = s.Substring(0,i)+ c[al_c++]+s.Substring(i+1);
        }

        // Return the sorted string
        return s;
    }

    // Driver code
    public static void Main()
    {
        string s = "d4c3b2a1";

        Console.WriteLine(sort(s));
    }
}

/* This code contributed by AnkitRai01 */

Javascript

<script>

// Javascript implementation of the approach

// Function that returns the string s
// in sorted form such that the
// positions of alphabets and numeric
// digits remain unchanged
function sort(s)
{
    var c = s.split('');

    c.sort();

    // Count of alphabets and numbers
    var al_c = 0, nu_c = 0;

    // Get the index from where the
    // alphabets start
    while (c[al_c].charCodeAt(0) < 97)
        al_c++;

    // Now replace the string with sorted string
    for (var i = 0; i < s.length; i++) {

        // If the position was occupied by an
        // alphabet then replace it with alphabet
        if (s[i].charCodeAt(0) < 97)
            s = s.substring(0,i)+ c[nu_c++]+s.substring(i+1);

        // Else replace it with a number
        else
        s = s.substring(0,i)+ c[al_c++]+s.substring(i+1);
    }

    // Return the sorted string
    return s;
}

// Driver code
var s = "d4c3b2a1";
document.write( sort(s));

// This code is contributed by rutvik_56.
</script>

Output

a1b2c3d4

Time complexity: O(N * log(N)) where N is the length of the string.
Auxiliary Space: O(N), where N is the length of the given string.