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[Coding Challenge] Secure My Conversation by Encryption and Decryption

Aniruddha Chaudhari/13941/2
Code
YouTube CSEstack

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

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 &amp;&amp; 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 &amp;&amp; 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

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

You can solve this coding question in any programming language. I choose Python as I feel more comfortable with it.

For more practice check other competitive coding challenge questions.

Python Interview Questions eBook

coding challenge
Aniruddha Chaudhari
I am complete Python Nut, love Linux and vim as an editor. I hold a Master of Computer Science from NIT Trichy. I dabble in C/C++, Java too. I keep sharing my coding knowledge and my own experience on CSEstack.org portal.

Your name can also be listed here. Got a tip? Submit it here to become an CSEstack author.

Comments

  • Reply
    Shivani Singh
    August 5, 2020 at 5:30 pm

    hey, I tried solving this question in c++.. but since I can’t test my code anywhere, feedbacks and corrections are welcome.

    • Reply
      Aniruddha Chaudhari
      August 6, 2020 at 10:56 pm

      Hi Shivani, I tested your code and it’s working. Awesome! I have added your code in our article.

      This will help many. Thanks for submitting your code.

      If you are interested to share your knowledge and contribute to our portal, kindly check here.

Leave a Reply Cancel reply

Why?

Why Competitive Programming Important?

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  14. Hailstone Sequence
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  16. Secure Conversation by Encry/Decry
  17. Special Elements in Matrix
  18. Next Greater No with Same set of Digits
  19. Smallest Subarray with Sum Greater than Given Number
  20. Group Anagrams
  21. Find Duplicates in Array in O(n)
  22. Find Two Unique Numbers from Array in O(n)
  23. Number Patterns & Finding Smallest Number
  24. Minimum Cost of Merging Files [Amazon]
  25. Minimum Distance for Truck to Deliver Order [Amazon]
  26. Minimum Coins Required
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  30. Longest Path in a Weighted Tree
  31. Generate Balanced Parentheses
  32. PostOrder Traversal Without Recursion

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