Decrypt message from given code by replacing all * with prefix values of encoded string

Last Updated : 29 Dec, 2021

Given a string str of length of N that is in the encoded form with alphabets and * . The task is to find the string from which it was generated. The required string can be generated from the encoded string by replacing all the * with the prefix values of the encoded string.

Examples:

Input: str = ab*c*d
Output: “ababcababcd”
Explanation: For the first occurrence of “*”, “ab” is the prefix. So ‘*’ is replaced by “ab” resulting the string to be “ababc*d” and for the next ‘*‘ the prefix is “ababc”. So the string will now change from “ababc*d” to “ababcababcd”.

Input : str = “z*z*z”
Output: zzzzzzz

Approach: The solution is based on greedy approach. Follow the steps mentioned below to solve the problem:

Consider an empty string result.
Iterate over the given coded string.
- if the current character in the string is not “*” then add the current character to the result.
- Otherwise, if the current character is “*”, add the result string formed till now with itself.
Return the result.

Below is the implementation of the given approach.

C++

// C++ code to implement above approach 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to return a string 
// found from the coded string 
string findstring(string str) 
{ 
    // Declaring string to store result 
    string result = ""; 
  
    // Loop to generate the original string 
    for (int i = 0; str[i] != '\0'; i++) { 
        // If current character in string 
        // is '*' add result to itself 
        if (str[i] == '*') 
            result += result; 
  
        // Else add current element only 
        else
            result += str[i]; 
    } 
    // Return the result 
    return result; 
} 
  
// Driver code 
int main() 
{ 
    string str = "ab*c*d"; 
    cout << findstring(str); 
    return 0; 
}

Java

// Java code to implement above approach 
class GFG { 
  
    // Function to return a string 
    // found from the coded string 
    static String findstring(String str) 
    { 
  
        // Declaring string to store result 
        String result = ""; 
  
        // Loop to generate the original string 
        for (int i = 0; i < str.length(); i++) { 
  
            // If current character in string 
            // is '*' add result to itself 
            if (str.charAt(i) == '*') 
                result += result; 
  
            // Else add current element only 
            else
                result += str.charAt(i); 
        } 
  
        // Return the result 
        return result; 
    } 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        String str = "ab*c*d"; 
        System.out.println(findstring(str)); 
    } 
} 
  
// This code is contributed by ukasp.

Python3

# Python code for the above approach 
  
# Function to return a string 
# found from the coded string 
def findstring(str): 
    
    # Declaring string to store result 
    result = "" 
  
    # Loop to generate the original string 
    for i in range(len(str)): 
        
        # If current character in string 
        # is '*' add result to itself 
        if (str[i] == '*'): 
                result += result 
  
        # Else add current element only 
        else: 
                result += str[i] 
    # Return the result 
    return result 
  
# Driver code 
str = "ab*c*d"
print(findstring(str)) 
  
# This code is contributed by Saurabh Jaiswal

C#

// C# code to implement above approach 
using System; 
class GFG 
{ 
  
  // Function to return a string 
  // found from the coded string 
  static string findstring(string str) 
  { 
  
    // Declaring string to store result 
    string result = ""; 
  
    // Loop to generate the original string 
    for (int i = 0; i < str.Length; i++) 
    { 
  
      // If current character in string 
      // is '*' add result to itself 
      if (str[i] == '*') 
        result += result; 
  
      // Else add current element only 
      else
        result += str[i]; 
    } 
  
    // Return the result 
    return result; 
  } 
  
  // Driver code 
  public static void Main() 
  { 
    string str = "ab*c*d"; 
    Console.Write(findstring(str)); 
  
  } 
} 
  
// This code is contributed by Samim Hossain Mondal.

Javascript

<script> 
   // JavaScript code for the above approach 
 
 
   // Function to return a string 
   // found from the coded string 
   function findstring(str) { 
     // Declaring string to store result 
     let result = ""; 
 
     // Loop to generate the original string 
     for (let i = 0; i < str.length; i++) { 
       // If current character in string 
       // is '*' add result to itself 
       if (str[i] == '*') 
         result += result; 
 
       // Else add current element only 
       else
         result += str[i]; 
     } 
     // Return the result 
     return result; 
   } 
 
   // Driver code 
 
   let str = "ab*c*d"; 
   document.write(findstring(str)); 
 
 // This code is contributed by Potta Lokesh 
 </script>