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 

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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: 

4

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

Space Complexity: O(1)