Find i'th Index character in a binary string obtained after n iterations

Last Updated : 08 Dec, 2023

Given a decimal number m, convert it into a binary string and apply n iterations. In each iteration, 0 becomes "01" and 1 becomes "10". Find the (based on indexing) index character in the string after the nth iteration.

Examples:

Input : m = 5, n = 2, i = 3
Output : 1
Input : m = 3, n = 3, i = 6
Output : 1

Change a decimal number into a binary and store it in string s.
Run loop n times in each iteration. Run another loop of string length s to convert 0 to "01" and 1 to "10" and store in another string s1. After completion of each iteration, assign string s1 to s.
Finally, return the value of the ith index in string s.

Implementation:

C++

// C++ Program to find ith character in 
// a binary string.
#include <bits/stdc++.h>
using namespace std;

// Function to store binary Representation
void binary_conversion(string &s, int m) {
  while (m) {
    int tmp = m % 2;
    s += tmp + '0';
    m = m / 2;
  }
  reverse(s.begin(), s.end());
}

// Function to find ith character
int find_character(int n, int m, int i) {

  string s;

  // Function to change decimal to binary
  binary_conversion(s, m);

  string s1 = "";
  for (int x = 0; x < n; x++) {
    for (int y = 0; y < s.length(); y++) {
      if (s[y] == '1') 
        s1 += "10";
      else 
        s1 += "01";      
    }

    // Assign s1 string in s string
    s = s1;
    s1 = "";
  }
  return s[i] - '0';
}

// Driver Function
int main() {
  int m = 5, n = 2, i = 8;
  cout << find_character(n, m, i);
  return 0;
}

Java

// Java Program to find ith 
// character in a binary String.
import java.io.*;
import java.util.Arrays;

class GFG
{
static String s = "";
static String ReverseString(String s)
{
    char[] arr = s.toCharArray();
    for(int i = 0;
            i < arr.length / 2; i++)
    {
        char temp = arr[i]; 
        arr[i] = arr[arr.length - i -1]; 
        arr[arr.length - i - 1] = temp; 
    }
    return new String(arr);
}

// Function to store
// binary Representation
static void binary_conversion(int m) 
{
    while (m != 0) 
    {
        int tmp = m % 2;
        s += Integer.toString(tmp);
        m = (int)(m / 2);
    }
    
    s = ReverseString(s);
}

// Function to find 
// ith character
static int find_character(int n, 
                          int m, 
                          int i) 
{     
    // Function to change
    // decimal to binary
    binary_conversion(m);

    String s1 = "";
    for (int x = 0; x < n; x++) 
    {
        for (int y = 0; 
                 y < s.length(); y++) 
        {
            if (s.charAt(y) == '1') 
            s1 += "10";
            else
            s1 += "01";     
        }
        
        // Assign s1 String 
        // in s String
        s = s1;
        s1 = "";
    }
    
    return s.charAt(i) - '0';
}

// Driver Code
public static void main(String args[])
{
    int m = 5, n = 2, i = 8;
    System.out.print(
               find_character(n, m, i));
}
}

// This code is contributed by 
// Manish Shaw(manishshaw1)

Python3

# Python3 Program to find ith character in 
# a binary string.

# Function to store binary Representation
def binary_conversion(s, m):
    while(m):
        temp = m % 2
        s += str(temp)
        m = m // 2
    
    return s[::-1]

# Function to find ith character
def find_character(n, m, i):
    s = ""


# Function to change decimal to binary
    s = binary_conversion(s, m)
    s1 = ""

    for x in range(n):
        for j in range(len(s)):
            if s[j] == "1":
                s1 += "10"
            else:
                s1 += "01"

    # Assign s1 string in s string     
        s = s1
        s1 = ""
    e = ord(s[i])
    r = ord('0')

    return e-r

# Driver code
m, n, i = 5, 2, 8

print(find_character(n,m,i))

# This code is contributed by mohit kumar 29

// C# Program to find ith 
// character in a binary string.
using System;

class GFG
{
    static string ReverseString(string s)
    {
        char[] arr = s.ToCharArray();
        Array.Reverse(arr);
        return new string(arr);
    }
    
    // Function to store
    // binary Representation
    static void binary_conversion(ref string s, 
                                  int m) 
    {
        while (m != 0) 
        {
            int tmp = m % 2;
            s += tmp.ToString();
            m = (int)(m / 2);
        }
        
        s = ReverseString(s);
    }
    
    // Function to find 
    // ith character
    static int find_character(int n, 
                              int m, int i) 
    {     
        string s = "";

        // Function to change
        // decimal to binary
        binary_conversion(ref s, m);

        string s1 = "";
        for (int x = 0; x < n; x++) 
        {
            for (int y = 0; y < s.Length; y++) 
            {
                if (s[y] == '1') 
                s1 += "10";
                else
                s1 += "01";     
            }
            
            // Assign s1 string 
            // in s string
            s = s1;
            s1 = "";
        }
        
        return s[i] - '0';
    }

    // Driver Code
    static void Main()
    {
        int m = 5, n = 2, i = 8;
        Console.Write(find_character(n, m, i));
    }
}

// This code is contributed by 
// Manish Shaw(manishshaw1)

JavaScript

<script>
// Javascript Program to find ith 
// character in a binary String.

let  s = "";

function ReverseString(s)
{
    let arr = s.split("");
    for(let i = 0;
            i < arr.length / 2; i++)
    {
        let temp = arr[i]; 
        arr[i] = arr[arr.length - i -1]; 
        arr[arr.length - i - 1] = temp; 
    }
    return arr.join("");
}

// Function to store
// binary Representation
function binary_conversion(m)
{
    while (m != 0) 
    {
        let tmp = m % 2;
        s += tmp.toString();
        m = Math.floor(m / 2);
    }
      
    s = ReverseString(s);
}

// Function to find 
// ith character
function find_character(n,m,i)
{
    // Function to change
    // decimal to binary
    binary_conversion(m);
  
    let s1 = "";
    for (let x = 0; x < n; x++) 
    {
        for (let y = 0; 
                 y < s.length; y++) 
        {
            if (s[y] == '1') 
                s1 += "10";
            else
                s1 += "01";     
        }
          
        // Assign s1 String 
        // in s String
        s = s1;
        s1 = "";
    }
      
    return s[i] - '0';
}

// Driver Code
let m = 5, n = 2, i = 8;
document.write(find_character(n, m, i));


// This code is contributed by patel2127
</script>

PHP

<?php

// Function to store binary Representation
function binaryConversion($s, $m) {
    while ($m) {
        $temp = $m % 2;
        $s .= strval($temp);
        $m = (int)($m / 2);
    }
    
    return strrev($s);
}

// Function to find ith character
function findCharacter($n, $m, $i) {
    $s = "";

    // Function to change decimal to binary
    $s = binaryConversion($s, $m);
    $s1 = "";

    for ($x = 0; $x < $n; $x++) {
        for ($j = 0; $j < strlen($s); $j++) {
            if ($s[$j] == "1") {
                $s1 .= "10";
            } else {
                $s1 .= "01";
            }
        }

        // Assign s1 string to s string     
        $s = $s1;
        $s1 = "";
    }

    $e = ord($s[$i]);
    $r = ord('0');

    return $e - $r;
}

// Driver code
$m = 5;
$n = 2;
$i = 8;

echo findCharacter($n, $m, $i);

?>

Output

Time complexity : O(|S|*2^n)
Auxiliary Space : O(n)

Refer Set-2 for an optimized solution.

All substrings of a given String

Mr.Gera

Improve

Article Tags :

Practice Tags :

Find i'th Index character in a binary string obtained after n iterations

Similar Reads

Strings in different language

Basic operations on String

Binary String

Substring and Subsequence

Palindrome

Thank You!

What kind of Experience do you want to share?