Find k’th character of decrypted string | Set 1

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"

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++

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// 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;
}

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Java














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// 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 



















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Python3














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# 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 



















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C#














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// 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 



















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Output:


e








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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