Odd numbers in N-th row of Pascal’s Triangle

Given N, the row number of Pascal’s triangle(row starting from 0). Find the count of odd numbers in the N-th row of Pascal’s Triangle.
Prerequisite: Pascal’s Triangle | Count number of 1’s in binary representation of N

Examples: 

Input : 11
Output : 8

Input : 20
Output : 4 

Approach: It appears the answer is always a power of 2. In fact, the following theorem exists: 
THEOREM: The number of odd entries in row N of Pascal’s Triangle is 2 raised to the number of 1’s in the binary expansion of N. 
Example: Since 83 = 64 + 16 + 2 + 1 has binary expansion (1010011), then row 83 has pow(2, 4) = 16 odd numbers.

Below is the implementation of the above approach:

C++

// CPP code to find the count of odd numbers
// in n-th row of Pascal's Triangle
#include <bits/stdc++.h>
using namespace std ;

/* Function to get no of set
   bits in binary representation
   of positive integer n */
int countSetBits(int n)
{
    unsigned int count = 0;
    while (n)
    {
        count += n & 1;
        n >>= 1;
    }

    return count;
}

int countOfOddsPascal(int n)
{
    // Count number of 1's in binary
    // representation of n.
    int c = countSetBits(n);

    // Number of odd numbers in n-th
    // row is 2 raised to power the count.
    return pow(2, c);
}

// Driver code
int main()
{
    int n = 20;
    cout << countOfOddsPascal(n) ;
    return 0;
}

Java

// Java code to find the count of odd
// numbers in n-th row of Pascal's
// Triangle
import java.io.*;

class GFG {

    /* Function to get no of set
    bits in binary representation
    of positive integer n */
    static int countSetBits(int n)
    {
        long count = 0;
        while (n > 0)
        {
            count += n & 1;
            n >>= 1;
        }

        return (int)count;
    }

    static int countOfOddsPascal(int n)
    {

        // Count number of 1's in binary
        // representation of n.
        int c = countSetBits(n);

        // Number of odd numbers in n-th
        // row is 2 raised to power the
        // count.
        return (int)Math.pow(2, c);
    }

    // Driver code
    public static void main (String[] args)
    {
        int n = 20;
        System.out.println(
                     countOfOddsPascal(n));
    }
}

// This code is contributed by anuj_67.

Python3

# Python code to find the count of
# odd numbers in n-th row of
# Pascal's Triangle

# Function to get no of set
# bits in binary representation
# of positive integer n
def countSetBits(n):
    count =0
    while n:
        count += n & 1
        n >>= 1

    return count

def countOfOddPascal(n):

    # Count number of 1's in binary
    # representation of n.
    c = countSetBits(n)

    # Number of odd numbers in n-th
    # row is 2 raised to power the count.
    return pow(2, c)

# Driver Program
n = 20
print(countOfOddPascal(n))

# This code is contributed by Shrikant13

C#

// C# code to find the count of odd numbers
// in n-th row of Pascal's Triangle
using System;

class GFG {

    /* Function to get no of set
    bits in binary representation
    of positive integer n */
    static int countSetBits(int n)
    {
        int count = 0;
        while (n > 0)
        {
            count += n & 1;
            n >>= 1;
        }

        return count;
    }

    static int countOfOddsPascal(int n)
    {
        // Count number of 1's in binary
        // representation of n.
        int c = countSetBits(n);

        // Number of odd numbers in n-th
        // row is 2 raised to power the
        // count.
        return (int)Math.Pow(2, c);
    }

    // Driver code
    public static void Main ()
    {
        int n = 20;
        Console.WriteLine(
                 countOfOddsPascal(n)) ;
    }
}

// This code is contributed by anuj_67.

PHP

<?php
// PHP code to find the
// count of odd numbers
// in n-th row of Pascal's
// Triangle

/* Function to get no of set
   bits in binary representation
   of positive integer n */
function countSetBits($n)
{
    $count = 0;
    while ($n)
    {
        $count += $n & 1;
        $n >>= 1;
    }

    return $count;
}

function countOfOddsPascal($n)
{

    // Count number of 1's in binary
    // representation of n.
    $c = countSetBits($n);

    // Number of odd numbers in n-th
    // row is 2 raised to power the count.
    return pow(2, $c);
}

    // Driver code
    $n = 20;
    echo countOfOddsPascal($n) ;

// This code is contributed by mits.
?>

Javascript

<script>
    // Javascript code to find the count of odd numbers
    // in n-th row of Pascal's Triangle

    /* Function to get no of set
    bits in binary representation
    of positive integer n */
    function countSetBits(n)
    {
        let count = 0;
        while (n > 0)
        {
            count += n & 1;
            n >>= 1;
        }

        return count;
    }

    function countOfOddsPascal(n)
    {
        // Count number of 1's in binary
        // representation of n.
        let c = countSetBits(n);

        // Number of odd numbers in n-th
        // row is 2 raised to power the
        // count.
        return Math.pow(2, c);
    }

    let n = 20;
    document.write(countOfOddsPascal(n)) ;

</script>

Output:

4

Time Complexity: O(L), where L is the length of a binary representation of a given N. 

Space Complexity: O(1)