Sort groups of numbers and characters separately in a String

Given a string str of alphanumeric characters, the task is to sort the similar group of consecutive characters separately and print the modified string i.e. all consecutive groups of digits and alphabetical characters will be sorted separately.

Examples:

Input: str = “121geeks21”
Output: 112eegks12
“121”, “geeks”, “21” are the valid groups
and they will be sorted separately.

Input: str = “cba321ab”
Output: abc123ab

Approach: Create a vector to store the starting indices of all the valid groups in the given string. Now, traverse the string character by character and if the current character is from a different group than the previous character then push the current index to the vector. After the string has been traversed completely, sort all the individual groups of substring of the given string using the vector updated earlier. Finally, print the modified string.

Below is the implementation of the above approach:

// C++ implementation of the approach 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to return the modified string 
string get_string(string str, int n) 
{ 
  
    // To store the previous character 
    char prev = str[0]; 
  
    // To store the starting indices 
    // of all the groups 
    vector<int> result; 
  
    // Starting index of the first group 
    result.push_back(0); 
  
    for (int i = 1; i < n; i++) { 
  
        // If the current character and the 
        // previous character differ 
        if (isdigit(str[i]) != isdigit(prev)) { 
  
            // Push the starting index 
            // of the new group 
            result.push_back(i); 
        } 
  
        // The current character now becomes previous 
        prev = str[i]; 
    } 
  
    // Sort the first group 
    sort(str.begin(), str.begin() + result[0]); 
  
    // Sort all the remaining groups 
    for (int i = 0; i < result.size() - 1; i++) { 
        sort(str.begin() + result[i], 
             str.begin() + result[i + 1]); 
    } 
  
    // Sort the last group 
    sort(str.begin() + result[result.size() - 1], 
         str.end()); 
  
    // Return the modified string 
    return str; 
} 
  
// Driver code 
int main() 
{ 
    string str = "121geeks21"; 
    int n = str.length(); 
  
    cout << get_string(str, n); 
  
    return 0; 
} 

Output:

112eegks12

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