Find k'th character of decrypted string

Given an encoded string where repetitions of substrings are represented as substring followed by count of substrings. For example, if encrypted string is “ab2cd2” and k=4 , so output will be ‘b’ because decrypted string is “ababcdcd” and 4th character is ‘b’.

Note: Frequency of encrypted substring can be of more than one digit. For example, in “ab12c3”, ab is repeated 12 times. No leading 0 is present in frequency of substring.

Examples:

Input: "a2b2c3", k = 5
Output: c
Decrypted string is "aabbccc"

Input : "ab4c2ed3", k = 9
Output : c
Decrypted string is "ababababccededed"

Input: "ab4c12ed3", k = 21
Output: e
Decrypted string is "ababababccccccccccccededed"

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

The idea is simple. Initially take empty decrypted string then decompress the string by reading substring and it’s frequency one by one and append current substring in decrypted string by it’s frequency. Repeat the process till the end of string and print the K’th character from decrypted string.

C++

// C++ program to find K'th character in 
// decrypted string 
#include<bits/stdc++.h> 
using namespace std; 
  
// Function to find K'th character in Encoded String 
char encodedChar(string str,int k) 
{ 
    // expand string variable is used to 
    // store final string after decompressing string str 
    string expand = ""; 
  
    string temp;  // Current substring 
    int freq = 0; // Count of current substring 
  
    for (int i=0; str[i]!='\0'; ) 
    { 
        temp = ""; // Current substring 
        freq = 0; // count frequency of current substring 
  
        // read characters untill you find a number 
        // or end of string 
        while (str[i]>='a' && str[i]<='z') 
        { 
            // push character in temp 
            temp.push_back(str[i]); 
            i++; 
        } 
  
        // read number for how many times string temp 
        // will be repeated in decompressed string 
        while (str[i]>='1' && str[i]<='9') 
        { 
            // generating frequency of temp 
            freq = freq*10 + str[i] - '0'; 
            i++; 
        } 
  
        // now append string temp into expand 
        // equal to its frequency 
        for (int j=1; j<=freq; j++) 
            expand.append(temp); 
    } 
  
    // this condition is to handle the case 
    // when string str is ended with alphabeds 
    // not with numeric value 
    if (freq==0) 
        expand.append(temp); 
  
    return expand[k-1]; 
} 
  
// Driver program to test the string 
int main() 
{ 
    string str = "ab4c12ed3"; 
    int k = 21; 
    cout << encodedChar(str, k) << endl; 
    return 0; 
} 

Java

// Java program to find K'th character in 
// decrypted string 
public class GFG { 
       
    // Function to find K'th character in  
    // Encoded String 
    static char encodedChar(String str,int k) 
    { 
        // expand string variable is used to 
        // store final string after decompressing  
        // string str 
        String expand = ""; 
       
        String temp = "";  // Current substring 
        int freq = 0; // Count of current substring 
       
        for (int i=0; i < str.length() ; ) 
        { 
            temp = ""; // Current substring 
            freq = 0; // count frequency of current 
                      // substring 
       
            // read characters until you find a number 
            // or end of string 
            while (i < str.length() && str.charAt(i)>='a'
                                && str.charAt(i)<='z') 
            { 
                // push character in temp 
                temp += str.charAt(i); 
                i++; 
            } 
       
            // read number for how many times string temp 
            // will be repeated in decompressed string 
            while (i < str.length() && str.charAt(i)>='1'
                                && str.charAt(i)<='9') 
            { 
                // generating frequency of temp 
                freq = freq*10 + str.charAt(i) - '0'; 
                i++; 
            } 
       
            // now append string temp into expand 
            // equal to its frequency 
            for (int j=1; j<=freq; j++) 
                 expand += temp; 
        } 
       
        // this condition is to handle the case 
        // when string str is ended with alphabets 
        // not with numeric value 
        if (freq==0) 
            expand += temp; 
       
        return expand.charAt(k-1); 
    } 
       
    // Driver program to test the string 
    public static void main(String args[]) 
    { 
        String str = "ab4c12ed3"; 
        int k = 21; 
        System.out.println(encodedChar(str, k)); 
    } 
} 
// This code is contributed by Sumit Ghosh 

Python3

# Python 3 program to find K'th character  
# in decrypted string 
  
# Function to find K'th character  
# in Encoded String 
def encodedChar(str, k): 
      
    # expand string variable is used  
    # to store final string after  
    # decompressing string str 
    expand = "" 
  
    # Current substring 
    freq = 0 # Count of current substring 
    i = 0
    while(i < len(str)): 
        temp = "" # Current substring 
        freq = 0 # count frequency of current substring 
  
        # read characters untill you find  
        # a number or end of string 
        while (i < len(str) and
               ord(str[i]) >= ord('a') and 
               ord(str[i]) <= ord('z')): 
                     
            # push character in temp 
            temp += str[i] 
            i += 1
  
        # read number for how many times string temp 
        # will be repeated in decompressed string 
        while (i < len(str) and 
               ord(str[i]) >= ord('1') and
               ord(str[i]) <= ord('9')): 
                     
            # generating frequency of temp 
            freq = freq * 10 + ord(str[i]) - ord('0') 
            i += 1
  
        # now append string temp into expand 
        # equal to its frequency 
        for j in range(1, freq + 1, 1): 
            expand += temp 
  
    # this condition is to handle the case 
    # when string str is ended with alphabeds 
    # not with numeric value 
    if (freq == 0): 
        expand += temp 
  
    return expand[k - 1] 
  
# Driver Code 
if __name__ == '__main__': 
    str = "ab4c12ed3"
    k = 21
    print(encodedChar(str, k)) 
  
# This code is contributed by 
# Shashank_Sharma 

C#

// C# program to find K'th  
// character in decrypted strinL 
using System; 
  
class GFG 
{ 
      
    // Function to find K'th 
    // character in Encoded String 
    static char encodedChar(string str, int k) 
    { 
        // expand string variable is  
        // used to store final string  
        // after decompressing string str 
        String expand = ""; 
      
        String temp = ""; // Current substring 
        int freq = 0; // Count of current substring 
      
        for (int i = 0; i < str.Length ; ) 
        { 
            temp = ""; // Current substring 
            freq = 0; // count frequency of current 
                      // substring 
      
            // read characters until you  
            // find a number or end of string 
            while (i < str.Length && str[i]>='a'
                                  && str[i]<='z') 
            { 
                // push character in temp 
                temp += str[i]; 
                i++; 
            } 
      
            // read number for how many times  
            // string temp will be repeated  
            // in decompressed string 
            while (i < str.Length && str[i] >= '1'
                                  && str[i] <= '9') 
            { 
                // generating frequency of temp 
                freq = freq * 10 + str[i] - '0'; 
                i++; 
            } 
      
            // now append string temp into  
            // expand equal to its frequency 
            for (int j = 1; j <= freq; j++) 
                expand += temp; 
        } 
      
        // this condition is to handle  
        // the case when string str is  
        // ended with alphabets not  
        // with numeric value 
        if (freq == 0) 
            expand += temp; 
      
        return expand[k - 1]; 
    } 
      
    // Driver Code 
    public static void Main() 
    { 
        string str = "ab4c12ed3"; 
        int k = 21; 
        Console.Write(encodedChar(str, k)); 
    } 
} 
  
// This code is contributed  
// by ChitraNayal 

Output:

Exercise : The above solution builds the decoded string to find k’th character. Extend the solution to work in O(1) extra space.

Find k-th character of decrypted string | Set – 2

This article is contributed by Shashank Mishra ( Gullu ) and reviewed by team GeeksforGeeks. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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My Personal Notes

Find k’th character of decrypted string | Set 1

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

C++

Java

Python3

C#

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