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Alphanumeric Abbreviations of a String
  • Difficulty Level : Hard
  • Last Updated : 29 Jul, 2017

Given a string of characters of length less than 10. We need to print all the alpha-numeric abbreviation of the string.

The alpha-numeric abbreviation is in the form of characters mixed with the digits which is equal to the number of skipped characters of a selected substring. So, whenever a substring of characters is skipped, you have to replace it with the digit denoting the number of characters in the substring. There may be any number of skipped substrings of a string. No two substrings should be adjacent to each other. Hence, no two digits are adjacent in the result. For a clearer idea, see the example.


Input : ANKS 
Output :
ANKS (nothing is replaced)
ANK1 (S is replaced) 
AN1S (K is replaced)
AN2  (KS is replaced)
A1KS (N is replaced)
A1K1 (N and S are replaced)
A2S (NK is replaced)
A3 (NKS is replaced)
1NKS (A is replaced)
1NK1 (A and S are replaced)
1N1S (A and N is replaced)
1N2 (A and KS are replaced)
2KS (AN is replaced)
2K1 (AN and S is replaced)
3S (ANK is replaced)
4 (ANKS is replaced)

Input : ABC
Output : 
Note: 11C is not valid because no two digits should be adjacent, 
2C is the correct one because AB is a substring, not A and B individually

Source: Google Interview question

The idea is to start with empty string. At every step, we have two choices.

  1. Consider character as it is.
  2. Add character to count. If there is no count, then use 1.


You can see how each character can either add up to the result as a character or as a digit. This further gives rise to 2^n abbreviations at the end where n is the length of string.

// C++ program to print all Alpha-Numeric Abbreviations
// of a String
#include <bits/stdc++.h>
using namespace std;
// Recursive function to print the valid combinations
// s is string, st is resultant string
void printCompRec(const string& s, int index,
                  int max_index, string st)
    // if the end of the string is reached
    if (index == max_index) {
        cout << st << "\n";
    // push the current character to result
    // recur for the next [Using Char]
    printCompRec(s, index + 1, max_index, st);
    // remove the character from result
    // set count of digits to 1
    int count = 1;
    // addition the adjacent digits
    if (!st.empty()) {
        if (isdigit(st.back())) {
            // get the digit and increase the count
            count += (int)(st.back() - '0');
            // remove the adjacent digit
    // change count to a character
    char to_print = (char)(count + '0');
    // add the character to result
    // recur for this again [Using Count]
    printCompRec(s, index + 1, max_index, st);
// Wrapper function
void printComb(std::string s)
    // if the string is empty
    if (!s.length())
    // Stores result strings one one by one
    string st;
    printCompRec(s, 0, s.length(), st);
// driver function
int main()
    string str = "GFG";
    return 0;



Source: CareerCup

This article is contributed by Aditya Nihal Kumar Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using or mail your article to See your article appearing on the GeeksforGeeks main page and help other Geeks.

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