Recursive program to insert a star between pair of identical characters

Given a string with repeated characters, we have to insert a star i.e.” * “ between pair of adjacent identical characters using recursion.

Examples:

Input : aabb 
Output : a*ab*b

Input : xxxy
Output : x*x*xy

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

Approach:

• If there is an empty string then simply return. This forms our base condition.
Else we do the following-
• Check if the first two characters are identical. If yes, then insert ” * ” between them.
• As we have now checked for identical characters at first two positions of the string so we now make a recursive call without the first character of the string.

The above approach has been implemented below:

• C

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// Recursive CPP program to insert * between // two consecutive same characters. #include <iostream> using namespace std;    // Function to insert * at desired position void pairStar(string& input, string& output,               int i = 0) {     // Append current character     output = output + input[i];        // If we reached last character     if (i == input.length() - 1)         return;        // If next character is same,      // append '*'     if (input[i] == input[i + 1])          output = output + '*';               pairStar(input, output, i+1); }    // Driver code int main() {     string input = "geeks", output = "";     pairStar(input, output);     cout << output << endl;     return 0; }

Output:

ge*eks

Note:The recursive function in the above code is tail recursive as recursive call is the last thing executed by the function.