Program to find the kth character after decrypting a string

Given a string str consisting of characters and numbers and an integer k, the task is to decrypt the string and the return the k^th character in the decrypted string.

In order to decrypt the string, traverse the string character by character and if the current character is an alphabet then append it to the resultant string else if it is a numeric digit then parse the number and repeat the resultant string this parsed number of times and continue with the original string. For example, str = “ab2c3” will be decrypted as “ababcababcababc”.

Examples:

Input: str = “ab2c3”, k = 5
Output: c
Decrypted string will be “ababcababcababc” and ‘c’ is the fifth character.

Input: str = “x2y3”, k = 3
Output: y

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

Initialize starting index i = 0 and total_len = 0.
Loop while i is less then the length of the input string and check if current character is an alphabet or not. If yes then increment total_len by 1 and check if total length is less then or equal to k if yes then return the string else increment i.
Initialize n = 0 again loop while i is less then length of input string and i is not an alphabet and parse the number and increment i and find the next_total_len = total_len * n.
- If k < total_len then get the position of the character by initializing pos = k % total_len.
- If position is not found then update position = total_len and finally return the character at k^th position. If not found then return -1.

Below is the implementation of the above approach:

C++

// C++ implementation of the approach 
#include <cstdlib> 
#include <iostream> 
using namespace std; 
  
// Function to print kth character of 
// String s after decrypting it 
char findKthChar(string s, int k) 
{ 
  
    // Get the length of string 
    int len = s.length(); 
  
    // Initialise pointer to character 
    // of input string to zero 
    int i = 0; 
  
    // Total length of resultant string 
    int total_len = 0; 
  
    // Traverse the string from starting 
    // and check if each character is 
    // alphabet then increment total_len 
    while (i < len) { 
        if (isalpha(s[i])) { 
  
            total_len++; 
  
            // If total_leg equal to k then 
            // return string else increment i 
            if (total_len == k) 
                return s[i]; 
  
            i++; 
        } 
  
        else { 
  
            // Parse the number 
            int n = 0; 
            while (i < len && !isalpha(s[i])) { 
                n = n * 10 + (s[i] - '0'); 
                i++; 
            } 
  
            // Update next_total_len 
            int next_total_len = total_len * n; 
  
            // Get the position of kth character 
            if (k <= next_total_len) { 
                int pos = k % total_len; 
  
                // Position not found then update 
                // position with total_len 
                if (!pos) { 
                    pos = total_len; 
                } 
  
                // Recursively find the kth position 
                return findKthChar(s, pos); 
            } 
            else { 
  
                // Else update total_len 
                // by next_total_len 
                total_len = next_total_len; 
            } 
        } 
    } 
  
    // Return -1 if character not found 
    return -1; 
} 
  
// Driver code 
int main() 
{ 
    string s = "ab2c3"; 
    int k = 5; 
  
    cout << findKthChar(s, k); 
  
    return 0; 
} 

Java

// Java implementation of the approach  
import java.util.*; 
class GfG  
{  
  
// Function to print kth character of  
// String s after decrypting it  
static Character findKthChar(String s, int k)  
{  
  
    // Get the length of string  
    int len = s.length();  
  
    // Initialise pointer to character  
    // of input string to zero  
    int i = 0;  
  
    // Total length of resultant string  
    int total_len = 0;  
  
    // Traverse the string from starting  
    // and check if each character is  
    // alphabet then increament total_len  
    while (i < len) 
    {  
        if (Character.isLetter(s.charAt(i))) 
        {  
  
            total_len++;  
  
            // If total_leg equal to k then  
            // return string else increment i  
            if (total_len == k)  
                return s.charAt(i);  
  
            i++;  
        }  
  
        else
        {  
  
            // Parse the number  
            int n = 0;  
            while (i < len && !Character.isLetter(s.charAt(i))) 
            {  
                n = n * 10 + (s.charAt(i) - '0');  
                i++;  
            }  
  
            // Update next_total_len  
            int next_total_len = total_len * n;  
  
            // Get the position of kth character  
            if (k <= next_total_len) 
            {  
                int pos = k % total_len;  
  
                // Position not found then update  
                // position with total_len  
                if (pos == 0) 
                {  
                    pos = total_len;  
                }  
  
                // Recursively find the kth position  
                return findKthChar(s, pos);  
            }  
            else 
            {  
  
                // Else update total_len  
                // by next_total_len  
                total_len = next_total_len;  
            }  
        }  
    }  
  
    // Return -1 if character not found  
    return ' ';  
}  
  
// Driver code  
public static void main(String[] args)  
{  
    String s = "ab2c3";  
    int k = 5;  
  
    System.out.println(findKthChar(s, k));  
} 
}  
  
// This code is contributed by Prerna Saini. 

Python3

# Python 3 implementation of the approach 
  
# Function to print kth character of 
# String s after decrypting it 
def findKthChar(s, k): 
      
    # Get the length of string 
    len1 = len(s) 
  
    # Initialise pointer to character 
    # of input string to zero 
    i = 0
  
    # Total length of resultant string 
    total_len = 0
  
    # Traverse the string from starting 
    # and check if each character is 
    # alphabet then increament total_len 
    while (i < len1): 
        if (s[i].isalpha()): 
            total_len += 1
  
            # If total_leg equal to k then 
            # return string else increment i 
            if (total_len == k): 
                return s[i] 
  
            i += 1
  
        else: 
              
            # Parse the number 
            n = 0
            while (i < len1 and s[i].isalpha() == False): 
                n = n * 10 + (ord(s[i]) - ord('0')) 
                i += 1
  
            # Update next_total_len 
            next_total_len = total_len * n 
  
            # Get the position of kth character 
            if (k <= next_total_len): 
                pos = k % total_len 
  
                # Position not found then update 
                # position with total_len 
                if (pos == 0): 
                    pos = total_len 
  
                # Recursively find the kth position 
                return findKthChar(s, pos) 
  
            else: 
                  
                # Else update total_len 
                # by next_total_len 
                total_len = next_total_len 
  
    # Return -1 if character not found 
    return -1
  
# Driver code 
if __name__ == '__main__': 
    s = "ab2c3"
    k = 5
  
    print(findKthChar(s, k)) 
      
# This code is contributed by 
# Surendra_Gangwar 

C#

// C# implementation of the approach  
using System;  
  
class GFG  
{  
  
// Function to print kth character of  
// String s after decrypting it  
static char findKthChar(String s, int k)  
{  
  
    // Get the length of string  
    int len = s.Length;  
  
    // Initialise pointer to character  
    // of input string to zero  
    int i = 0;  
  
    // Total length of resultant string  
    int total_len = 0;  
  
    // Traverse the string from starting  
    // and check if each character is  
    // alphabet then increament total_len  
    while (i < len) 
    {  
        if (char.IsLetter(s[i])) 
        {  
            total_len++;  
  
            // If total_leg equal to k then  
            // return string else increment i  
            if (total_len == k)  
                return s[i];  
  
            i++;  
        }  
  
        else
        {  
  
            // Parse the number  
            int n = 0;  
            while (i < len && !char.IsLetter(s[i])) 
            {  
                n = n * 10 + (s[i] - '0');  
                i++;  
            }  
  
            // Update next_total_len  
            int next_total_len = total_len * n;  
  
            // Get the position of kth character  
            if (k <= next_total_len) 
            {  
                int pos = k % total_len;  
  
                // Position not found then update  
                // position with total_len  
                if (pos == 0) 
                {  
                    pos = total_len;  
                }  
  
                // Recursively find the kth position  
                return findKthChar(s, pos);  
            }  
            else
            {  
  
                // Else update total_len  
                // by next_total_len  
                total_len = next_total_len;  
            }  
        }  
    }  
  
    // Return -1 if character not found  
    return ' ';  
}  
  
// Driver code  
public static void Main(String[] args)  
{  
    String s = "ab2c3";  
    int k = 5;  
  
    Console.WriteLine(findKthChar(s, k));  
} 
} 
  
// This code is contributed by PrinciRaj1992  

Output:

My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

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