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Find i’th Index character in a binary string obtained after n iterations
  • Difficulty Level : Medium
  • Last Updated : 08 Jul, 2019

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 ith(based indexing) index character in the string after 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 binary and store 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. At last Return the value of ith index in string s.

C++

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// 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;
}

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Java

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// 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)

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Python3

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# 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

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C#

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// 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)

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Output:

1

Refer Set-2 for an optimized solution.

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