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”

Input: str = “d4c3b2a1”
Output: a1b2c3d4

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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 ` `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 */`

Output:

```a1b2c3d4
```

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

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