Print all Possible Decodings of a given Digit Sequence

Given the numeric string str, where 1 represents ‘a’, 2 represents ‘b’, …, 26 represents ‘z’, the task is to print all possible alphabetical strings that can be obtained from str.

Examples:  

Input: str = “1123” 
Output: 
aabc 
kbc 
alc 
aaw 
kw 
Explanation: 
The given string can be splitted as: 
1) “1123” = “1” + “1” + “2” + “3” = aabc 
2) “1123” = “11” + “2” + “3” = kbc 
3) “1123” = “1” + “12” + “3” = alc 
4) “1123” = “1” + “1” + “23” = aaw 
5) “1123” = “11” + “23” = aabc
Input: str = “56” 
Output: 
ef 
Explanation: 
The given string can be splitted as: 
1) “56” = “5” + “6” = ef 
 

Approach: It can be observed that every single character represents an alphabet apart from 0. This problem is recursive and can be broken into sub-problems. The terminating condition will be when the passed string is empty. Below are the steps to solve the problem: 

  1. Create a helper function getChar() that returns the corresponding alphabet of the given numeric character.
  2. Create a recursive function that takes the input as a string and returns an array of the desired answer of every character extracted.
  3. The base case is when the input string is empty. Return an array of length one containing an empty string for this case.
  4. Extract every single character by using the helper function and append it to the empty string first and store it in an array, say output1.
  5. At the same time check if the length of the characters is greater than or equal to two and also check if the two characters extracted lies in the range of alphabets. Now, store the corresponding character in an array, say output2.
  6. Then create a final output array whose length will be the sum of the length of output1 and output2 and store their answers and return it.
  7. Repeat the above steps for every single or pair of adjacent characters extracted. Now, return the final array obtained.
  8. Traverse the array and for each string, generate corresponding strings of lowercase alphabets and print them.

Below is the implementation of the above approach: 

Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program for the above approach
 
import java.io.*;
 
class GFG {
 
    // Function to check if all the
    // characters are lowercase or not
    public static boolean
    nonLower(String s)
    {
        // Traverse the string
        for (int i = 0; i < s.length(); i++) {
 
            // If any character is not
            // found to be in lowerCase
            if (!Character
                     .isLowerCase(s.charAt(i))) {
                return true;
            }
        }
 
        return false;
    }
 
    // Function to print the decodings
    public static void
    printCodes(String output[])
    {
        for (int i = 0; i < output.length; i++) {
 
            // If all characters are not
            // in lowercase
            if (nonLower(output[i]))
                continue;
            System.out.println(output[i]);
        }
    }
 
    // Fuction to return the character
    // corresponding to given integer
    public static char getChar(int n)
    {
        return (char)(n + 96);
    }
 
    // Function to return the decodings
    public static String[] getCode(
        String str)
    {
        // Base case
        if (str.length() == 0) {
 
            String ans[] = { "" };
            return ans;
        }
 
        // Recursive call
        String output1[]
            = getCode(str.substring(1));
 
        // Stores the characters of
        // two digit numbers
        String output2[] = new String[0];
 
        // Extract first digit and
        // first two digits
        int firstDigit
            = (str.charAt(0) - '0');
        int firstTwoDigit = 0;
 
        if (str.length() >= 2) {
 
            firstTwoDigit
                = (str.charAt(0) - '0') * 10
                  + (str.charAt(1) - '0');
 
            // Check if it lies in the
            // range of alphabets
            if (firstTwoDigit >= 10
                && firstTwoDigit <= 26) {
 
                // Next recursive call
                output2
                    = getCode(str.substring(2));
            }
        }
 
        // Combine both the output in a
        // single final output array
        String output[]
            = new String[output1.length
                         + output2.length];
 
        // Index of final output array
        int k = 0;
 
        // Store the elements of output1
        // in final output array
        for (int i = 0; i < output1.length; i++) {
 
            char ch = getChar(firstDigit);
 
            output[i] = ch + output1[i];
            k++;
        }
 
        // Store the elements of output2
        // in final output array
        for (int i = 0; i < output2.length; i++) {
 
            char ch = getChar(firstTwoDigit);
 
            output[k] = ch + output2[i];
            k++;
        }
 
        // Result the result
        return output;
    }
 
    // Driver Code
    public static void main(String[] args)
    {
        String input = "101";
 
        // Function call
        String output[] = getCode(input);
 
        // Print function call
        printCodes(output);
    }
}

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program for
// the above approach
using System;
class GFG{
 
// Function to check if all the
// characters are lowercase or not
public static bool nonLower(String s)
{
  // Traverse the string
  for (int i = 0; i < s.Length; i++)
  {
    // If any character is not
    // found to be in lowerCase
    if (!char.IsLower(s[i]))
    {
      return true;
    }
  }
  return false;
}
 
// Function to print the decodings
public static void printCodes(String []output)
{
  for (int i = 0; i < output.Length; i++)
  {
    // If all characters are not
    // in lowercase
    if (nonLower(output[i]))
      continue;
    Console.WriteLine(output[i]);
  }
}
 
// Fuction to return the character
// corresponding to given integer
public static char getChar(int n)
{
  return (char)(n + 96);
}
 
// Function to return the decodings
public static String[] getCode(String str)
{
  // Base case
  if (str.Length == 0)
  {
    String []ans = { "" };
    return ans;
  }
 
  // Recursive call
  String []output1 = getCode(str.Substring(1));
 
  // Stores the characters of
  // two digit numbers
  String []output2 = new String[0];
 
  // Extract first digit and
  // first two digits
  int firstDigit = (str[0] - '0');
  int firstTwoDigit = 0;
 
  if (str.Length >= 2)
  {
    firstTwoDigit = (str[0] - '0') * 10 +
                    (str[1] - '0');
 
    // Check if it lies in the
    // range of alphabets
    if (firstTwoDigit >= 10 &&
        firstTwoDigit <= 26)
    {
      // Next recursive call
      output2 = getCode(str.Substring(2));
    }
  }
   
  // Combine both the output in a
  // single readonly output array
  String []output = new String[output1.Length +
                               output2.Length];
 
  // Index of readonly output array
  int k = 0;
 
  // Store the elements of output1
  // in readonly output array
  for (int i = 0; i < output1.Length; i++)
  {
    char ch = getChar(firstDigit);
    output[i] = ch + output1[i];
    k++;
  }
 
  // Store the elements of output2
  // in readonly output array
  for (int i = 0; i < output2.Length; i++)
  {
    char ch = getChar(firstTwoDigit);   
    output[k] = ch + output2[i];
    k++;
  }
 
  // Result the result
  return output;
}
 
// Driver Code
public static void Main(String[] args)
{
  String input = "101";
 
  // Function call
  String []output = getCode(input);
 
  // Print function call
  printCodes(output);
}
}
 
// This code is contributed by Rajput-Ji

chevron_right


Output: 

ja


 

Time Complexity: O(2N)
Space Complexity:O(N)

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.




My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Improved By : Rajput-Ji