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Add index to characters and reverse the string
  • Difficulty Level : Expert
  • Last Updated : 02 May, 2019

Given a string str, the task is to encrypt and reverse the string. The string is encrypted by adding every character of the string with it’s index in the string i.e. if character‘a’ is at index 2 then the character in the updated string will be ‘a’ + 2 = ‘c’. Since value of string may go beyond 256, do the addition under modulo 256.

Examples:

Input: str = “geeks”
Output: wngfg
‘g’ + 0 = ‘g’
‘e’ + 1 = ‘f’
‘e’ + 2 = ‘g’
‘k’ + 3 = ‘n’
‘s’ + 4 = ‘w’

Input: str = “java”
Output: dxbj

Approach:



  • Add every character of the string with its index within the same string.
  • Reverse the string.
  • Print the reversed string.

Below is the implementation of the above approach:

C++




// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
  
// Function to return the encryptet string
string getEncryptedString(string str)
{
  
    // To build the encrypted string
    string sb ="";
  
    // Traverse the string in reverse
    for (int i = str.length() - 1; i >= 0; i--) 
    {
        sb+=(char)((int)str[i] + i) % 256;
    }
  
    // Return the encrypted string
    return sb;
}
  
// Driver code
int main()
{
    string str = "geeks";
    cout<<getEncryptedString(str)<<endl;
    return 0;
      
}
  
// This code is contributed by mits

Java




// Java implementation of the approach
public class HelloWorld {
  
    // Function to return the encryptet string
    static String getEncryptedString(String str)
    {
  
        // To build the encrypted string
        StringBuilder sb = new StringBuilder("");
  
        // Traverse the string in reverse
        for (int i = str.length() - 1; i >= 0; i--) {
            sb.append("" + (char)((str.charAt(i) + i) % 256));
        }
  
        // Return the encrypted string
        return sb.toString();
    }
  
    // Driver code
    public static void main(String[] args)
    {
        String str = "geeks";
        System.out.println(getEncryptedString(str));
    }
}

Python3




# Python3 implementation of the approach
  
# Function to return the encryptet string
def getEncryptedString(str):
  
  
    # To build the encrypted string
    sb = "";
  
    # Traverse the string in reverse
    for i in range(len(str) - 1,-1,-1): 
        sb += chr((ord(str[i]) + i) % 256);
  
    # Return the encrypted string
    return sb;
  
# Driver code
str = "geeks";
print(getEncryptedString(str));
  
# This code is contributed by mits

C#




// C# implementation of the approach
using System;
using System.Text; 
  
public class HelloWorld 
{
  
    // Function to return the encryptet string
    static String getEncryptedString(String str)
    {
  
        // To build the encrypted string
        StringBuilder sb = new StringBuilder("");
  
        // Traverse the string in reverse
        for (int i = str.Length - 1; i >= 0; i--) 
        {
            sb.Append("" + (char)((str[i] + i) % 256));
        }
  
        // Return the encrypted string
        return sb.ToString();
    }
  
    // Driver code
    public static void Main(String[] args)
    {
        String str = "geeks";
        Console.WriteLine(getEncryptedString(str));
    }
}
  
// This code contributed by Rajput-Ji

PHP




<?php
// PHP implementation of the approach
  
// Function to return the encryptet string
function getEncryptedString($str)
{
  
    // To build the encrypted string
    $sb = "";
  
    // Traverse the string in reverse
    for ($i = strlen($str) - 1; $i >= 0; $i--) 
    {
        $sb .= chr((ord($str[$i]) + $i) % 256);
    }
  
    // Return the encrypted string
    return $sb;
}
  
// Driver code
$str = "geeks";
print(getEncryptedString($str));
  
// This code is contributed by mits
?>
Output:
wngfg

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