[Coding Challenge] Secure My Conversation by Encryption and Decryption

This is competitive coding question was asked in Goldman Sachs coding round. There were two coding questions which are needed to be solved in two hours.

Basically you can take one hour to solve this question.

Problem Statement: Secure My Conversation by Encryption and Decryption

Person A and B use an encryption-based system for their conversation.

Each conversation message is encrypted from the source and decrypted in the destination using a shared private positive number key known to each other.

The algorithm is illustrated with an example.

Input format with explanation:

1. Operation (1 for Encryption and 2 for Decryption)
2. Input message
3. Input private key

Output format with explanation:

1. Output message

Example 1:

Input:

1
Open
123

Output:

Oppeeen

Here, the input message characters are duplicated based on each digit in the key.

Example 2:

Input:

2
Oppeeen 
123

Output:

Open

Here, the input message characters are compressed based on each digit in the key.

The conversation message and the private key need NOT be in equal length and the encoding/decoding takes place till the end is reached either conversation message or private key while retaining the rest of the conversation message.

Programming Solution

Just don’t read the coding solution. To get the maximum out of it. Try to execute this code in our online compiler and understand the logic implemented.

Python Code

#!/bin/python3
 
import math
import os
import random
import re
import sys

# Complete the secureChannel function below.
def secureChannel(operation, message, key):
    if len(message)==0 or len(key)==0:
        return "-1"
 
    strRet=""
 
    if operation==1:
        index=0
        for keyVal in key:
            nKeyVal=int(keyVal)
            if index>=len(message):
                return strRet
            strRet=strRet+message[index]*nKeyVal
            index=index+1
        if index < len(message):
            strRet=strRet+message[index:]
 
    elif operation==2:
        index=0
        for keyVal in key:
            nKeyVal=int(keyVal)
            if index>=len(message):
                return strRet
            for i in range(0,nKeyVal):
                if (index+i)>=len(message):
                    return "-1"
                if message[index] != message[index+i]:
                    return "-1"
            strRet=strRet+message[index]
            index=index+nKeyVal
        if index < len(message):
            strRet=strRet+message[index:]
 
    else:
        return "-1"

    return strRet
 
if __name__ == '__main__':
    print(secureChannel(1, 'Open',  '123'))
    print(secureChannel(2, 'Oppeeen',  '123'))

To understand this code, you can refer Python Programming tutorial.

C++ Code

(This solution in C++ is shared by the Shivani Singh.)

#include <string>
#include <iostream>

using namespace std;

string encoding( string msg, string key)
{
  string ans;
  int i=0;//for msg
  int j=0;//for key
  int keysize = key.size();
  int msgsize= msg.size();
  if(keysize==0 || msgsize==0)
    return "";//to be defined in question
  while(j<keysize && i<msgsize)
  {
    int count= key[j]-'0';
    for(int it=0;it<count;it++)
      ans.push_back(msg[i]);
    j++; i++;
  }
  while(i< msgsize)
  {
    ans.push_back(msg[i]);
    i++;
  }
  return ans;
}

string decoding(string msg, string key)
{
  string ans;
  int i=0;//for msg
  int j=0;//for key
  int keysize = key.size();
  int msgsize= msg.size();
  if(keysize==0 || msgsize==0)
  return " ";//to be defined in question
  while(i<msgsize && j<keysize)
  {
    ans.push_back(msg[i]);
    i=i+(key[j]-'0');
    j++;
  }
  while(i<msgsize)
  {
    ans.push_back(msg[i]);
    i++;
  }
  return ans;
}

int main()
{
  string msg= "open";
  string key= "123";
  cout<<encoding(msg,key)<<endl;
  cout<<decoding("oppeeen","123");
  return 0;
}

To understand this code, refer C/C++ programming tutorial.

Output:

Oppeeen
Open

Java Code

(This solution in Java is shared by the Bharath Kalyan S.)

public static String EncryptMessage(String message, String key) {
        if (message.length() == 0 || key.length() == 0)
            return "";

        StringBuilder builder = new StringBuilder();
        int i = 0, j = 0;
        int messageLength = message.length();
        int keyLength = key.length();

        while (i < messageLength && j < keyLength) {
            char character = message.charAt(i);
            int repeat = key.charAt(j) - '0';
            for (int k = 0; k < repeat; k++) {
                builder.append(character);
            }
            i++;
            j++;
        }
        if (i != messageLength) {
            builder.append(message.substring(i));
        }

        return builder.toString();
    }

    public static String DecryptMessage(String encryptedMessage, String key) {
        if (encryptedMessage.length() == 0 || key.length() == 0)
            return "";

        StringBuilder builder = new StringBuilder();
        int i = 0, j = 0;
        int messageLength = encryptedMessage.length();
        int keyLength = key.length();

        while (j < keyLength) {
            char mainChar = encryptedMessage.charAt(i);
            builder.append(mainChar);
            i = i + key.charAt(j) - '0';
            j++;
        }

        builder.append(encryptedMessage.substring(i));
        return builder.toString();
    }

Refer complete Java tutorial.

The program is self-explanatory. If you have any doubt or finding it difficult to understand the code, kindly comment your query below.

You can solve this coding question in any programming language.

For more practice check other competitive coding challenge questions.

Aniruddha Chaudhari

I am a Python enthusiast who loves Linux and Vim. I hold a Master of Computer Science degree from NIT Trichy and have 10 years of experience in the IT industry, focusing on the Software Development Lifecycle from Requirements Gathering, Design, Development to Deployment. I have worked at IBM, Ericsson, and NetApp, and I share my knowledge on CSEstack.org.