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

  • Difficulty Level : Medium
  • Last Updated : 24 May, 2021

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

 

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

1. Change a decimal number into a binary and store it in string s. 
2. 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. 
3. Finally, return the value of the ith index in string s. 



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#




// 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>
Output: 
1

 

Refer Set-2 for an optimized solution. 
 

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