Decrypt the String according to given algorithm
Last Updated :
18 Aug, 2021
Given encrypted string str consisting of alphabets and numeric characters, the task is to decrypt the string and find the encrypted message.
In order to decrypt the message, find every cluster of numeric characters representing a single alphabetic character which can be obtained by calculating the modulus of the number with 26 and the found value from the range [0, 25] can be mapped with the characters ['a', 'z'].
For example, if str = "32ytAAcV4ui30hf10hj18" then the clusters of numeric characters will be {32, 4, 30, 10, 18} which gives {6, 4, 4, 10, 18} after performing modulus with 26 and can be mapped to {'g', 'e', 'e', 'k', 's'}
Examples:
Input: str = "this50hi4huji70"
Output: geeks
Input: str = "a1s2d3f3"
Output: bcdd
Approach: The idea is to traverse each character one by one in a string, then check if it is a numeric character or not. If it is then concatenate it into a string. Finally, modulo that number string with 26.
While doing modulo operation, we can't simply do x % 26 as the number can be too large and will result in an integer overflow.
To handle this, we will process all digits one by one and use the property that
(A * B) mod C = ((A mod C) * (B mod C)) mod C
Then, finally decode back each integer to character by 0, 1, 2, 3, ...25 to 'a', 'b', 'c', ...'z', concatenate all characters and print the final result.
Below is the implementation of the above approach:
C++
// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
const int MOD = 26;
// Function that returns (num % 26)
int modulo_by_26(string num)
{
// Initialize result
int res = 0;
// One by one process all digits of 'num'
for (int i = 0; i < num.length(); i++)
res = (res * 10 + (int)num[i] - '0') % MOD;
return res;
}
// Function to return the decrypted string
string decrypt_message(string s)
{
// To store the final decrypted answer
string decrypted_str = "";
string num_found_so_far = "";
// One by one check for each character
// if it is a numeric character
for (int i = 0; i < s.length(); ++i) {
if (s[i] >= '0' && s[i] <= '9') {
num_found_so_far += s[i];
}
else if (num_found_so_far.length() > 0) {
// Modulo the number found in the string by 26
decrypted_str += 'a'
+ modulo_by_26(num_found_so_far);
num_found_so_far = "";
}
}
if (num_found_so_far.length() > 0) {
decrypted_str += 'a'
+ modulo_by_26(num_found_so_far);
}
return decrypted_str;
}
// Driver code
int main()
{
string s = "32ytAAcV4ui30hf10hj18";
// Print the decrypted string
cout << decrypt_message(s);
return 0;
}
// Java implementation of the approach
import java.util.*;
class GFG{
static int MOD = 26;
// Function that returns (num % 26)
static int modulo_by_26(String num)
{
// Initialize result
int res = 0;
// One by one process all digits of 'num'
for(int i = 0; i < num.length(); i++)
{
res = ((res * 10 +
(int)num.charAt(i) - '0') % MOD);
}
return res;
}
// Function to return the decrypted String
static String decrypt_message(String s)
{
// To store the final decrypted answer
String decrypted_str = "";
String num_found_so_far = "";
// One by one check for each character
// if it is a numeric character
for(int i = 0; i < s.length(); ++i)
{
if (s.charAt(i) >= '0' && s.charAt(i) <= '9')
{
num_found_so_far += s.charAt(i);
}
else if (num_found_so_far.length() > 0)
{
// Modulo the number found in the String by 26
decrypted_str += (char)('a' +
modulo_by_26(num_found_so_far));
num_found_so_far = "";
}
}
if (num_found_so_far.length() > 0)
{
decrypted_str += (char)('a' +
modulo_by_26(num_found_so_far));
}
return decrypted_str;
}
// Driver code
public static void main(String[] args)
{
String s = "32ytAAcV4ui30hf10hj18";
// Print the decrypted string
System.out.print(decrypt_message(s));
}
}
// This code is contributed by amal kumar choubey
# Python3 implementation of
# the approach
MOD = 26
# Function that returns
# (num % 26)
def modulo_by_26(num):
# Initialize result
res = 0
# One by one process all
# digits of 'num'
for i in range(len(num)):
res = ((res * 10 + ord(num[i]) -
ord('0')) % MOD)
return res
# Function to return the
# decrypted string
def decrypt_message(s):
# To store the final
# decrypted answer
decrypted_str = ""
num_found_so_far = ""
# One by one check for
# each character if it
# is a numeric character
for i in range(len(s)):
if (s[i] >= '0' and
s[i] <= '9'):
num_found_so_far += s[i]
elif (len(num_found_so_far) > 0):
# Modulo the number found
# in the string by 26
decrypted_str += chr(ord('a') +
(modulo_by_26(num_found_so_far)))
num_found_so_far = ""
if (len(num_found_so_far) > 0):
decrypted_str += chr(ord('a') +
(modulo_by_26(num_found_so_far)))
return decrypted_str
# Driver code
if __name__ == "__main__":
s = "32ytAAcV4ui30hf10hj18"
# Print the decrypted string
print(decrypt_message(s))
# This code is contributed by Chitranayal
// C# implementation of the approach
using System;
class GFG{
static int MOD = 26;
// Function that returns (num % 26)
static int modulo_by_26(String num)
{
// Initialize result
int res = 0;
// One by one process all digits of 'num'
for(int i = 0; i < num.Length; i++)
{
res = ((res * 10 +
(int)num[i] - '0') % MOD);
}
return res;
}
// Function to return the decrypted String
static String decrypt_message(String s)
{
// To store the readonly decrypted answer
String decrypted_str = "";
String num_found_so_far = "";
// One by one check for each character
// if it is a numeric character
for(int i = 0; i < s.Length; ++i)
{
if (s[i] >= '0' && s[i] <= '9')
{
num_found_so_far += s[i];
}
else if (num_found_so_far.Length > 0)
{
// Modulo the number found
// in the String by 26
decrypted_str += (char)('a' +
modulo_by_26(num_found_so_far));
num_found_so_far = "";
}
}
if (num_found_so_far.Length > 0)
{
decrypted_str += (char)('a' +
modulo_by_26(num_found_so_far));
}
return decrypted_str;
}
// Driver code
public static void Main(String[] args)
{
String s = "32ytAAcV4ui30hf10hj18";
// Print the decrypted string
Console.Write(decrypt_message(s));
}
}
// This code is contributed by amal kumar choubey
<script>
// JavaScript implementation of the approach
let MOD = 26;
// Function that returns (num % 26)
function modulo_by_26(num)
{
// Initialize result
let res = 0;
// One by one process all digits of 'num'
for(let i = 0; i < num.length; i++)
{
res = ((res * 10 +
num[i].charCodeAt(0) - '0'.charCodeAt(0)) % MOD);
}
return res;
}
// Function to return the decrypted String
function decrypt_message(s)
{
// To store the final decrypted answer
let decrypted_str = "";
let num_found_so_far = "";
// One by one check for each character
// if it is a numeric character
for(let i = 0; i < s.length; ++i)
{
if (s[i].charCodeAt(0) >= '0'.charCodeAt(0) &&
s[i].charCodeAt(0) <= '9'.charCodeAt(0))
{
num_found_so_far += s[i];
}
else if (num_found_so_far.length > 0)
{
// Modulo the number found in the String by 26
decrypted_str += String.fromCharCode('a'.charCodeAt(0) +
modulo_by_26(num_found_so_far));
num_found_so_far = "";
}
}
if (num_found_so_far.length > 0)
{
decrypted_str += String.fromCharCode('a'.charCodeAt(0) +
modulo_by_26(num_found_so_far));
}
return decrypted_str;
}
// Driver code
let s = "32ytAAcV4ui30hf10hj18";
// Print the decrypted string
document.write(decrypt_message(s));
// This code is contributed by rag2127
</script>
Time Complexity: O(N)
Auxiliary Space: O(N)
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