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Find most significant bit of a number X in base Y

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  • Last Updated : 20 Apr, 2021

Given two positive integers X and Y, the task is to find the MSB of X, in the given base Y.
Examples:

Input: X = 55, Y = 3 
Output:
Explanation: 
55 is 2001 in base 3 with first digit as 2.
Input: X = 123, Y = 10 
Output:
Explanation: 
123 is 123 in base 10 with first digit 1. 

Approach: Let the task to find 1st digit of X = 1234 in base Y = 10, So to get First digit = 1:  

Divide 1234 by 1000 
= X / 103 
= X / 10Number of Digits in X – 1 
= X / 10log(X) / log(10) (which is for base 10)  

For any other base, we can replace 10 with Y. Therefore, we can calculate the first digit of a number X in base Y by using the formula:

X / Y(log(X)/log(Y))

Below is the implementation of the above approach:  

C++




// C++ Program to find the
// first digit of X in base Y
 
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the first
// digit of X in base Y
void first_digit(int x, int y)
{
    // calculating number of digits of
    // x in base y
    int length = log(x) / log(y) + 1;
 
    // finding first digit of x in base y
    int first_digit = x / pow(y, length - 1);
 
    cout << first_digit;
}
 
// Driver code
int main()
{
    int X = 55, Y = 3;
 
    first_digit(X, Y);
 
    return 0;
}

Java




// Java Program to find the
// first digit of X in base Y
import java.util.*;
class GFG{
 
// Function to find the first
// digit of X in base Y
static void first_digit(int x, int y)
{
    // calculating number of digits of
    // x in base y
    int length = (int)(Math.log(x) /
                       Math.log(y) + 1);
 
    // finding first digit of x in base y
    int first_digit = (int)(x / Math.pow(y,
                                length - 1));
 
    System.out.println(first_digit);
}
 
// Driver code
public static void main(String args[])
{
    int X = 55, Y = 3;
 
    first_digit(X, Y);
}
}
 
// This code is contributed by AbhiThakur

Python3




# Python3 program to find the
# first digit of X in base Y
import math
 
# Function to find the first
# digit of X in base Y
def first_digit(x, y):
     
    # Calculating number of digits of
    # x in base y
    length = int (math.log(x) /
                  math.log(y) + 1)
     
    # Finding first digit of x in base y
    first_digit = x / math.pow(y, length - 1)
 
    print(int(first_digit))
     
# Driver code
X = 55
Y = 3
 
first_digit(X, Y)
 
# This code is contributed by ishayadav181

C#




// C# Program to find the
// first digit of X in base Y
using System;
class GFG{
 
// Function to find the first
// digit of X in base Y
static void first_digit(int x, int y)
{
    // calculating number of digits of
    // x in base y
    int length = (int)(Math.Log(x) /
                       Math.Log(y) + 1);
 
    // finding first digit of x in base y
    int first_digit = (int)(x / Math.Pow(y,
                                length - 1));
 
    Console.Write(first_digit);
}
 
// Driver code
public static void Main()
{
    int X = 55, Y = 3;
 
    first_digit(X, Y);
}
}
 
// This code is contributed by Akanksha_Rai

Javascript




<script>
 
// Javascript Program to find the
// first digit of X in base Y
 
// Function to find the first
// digit of X in base Y
function first_digit(x, y)
{
    // calculating number of digits of
    // x in base y
    var length = parseInt(Math.log(x) / Math.log(y)) + 1;
 
    // finding first digit of x in base y
    var first_digit = parseInt(x / Math.pow(y, length - 1));
 
    document.write( first_digit);
}
 
// Driver code
var X = 55, Y = 3;
first_digit(X, Y);
 
</script>

Output: 

2

 

Time Complexity: O(1)

Auxiliary Space: O(1)


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