Python Program to Count set bits in an integer

Write an efficient program to count number of 1s in binary representation of an integer.

Examples :

Input : n = 6
Output : 2
Binary representation of 6 is 110 and has 2 set bits

Input : n = 13
Output : 3
Binary representation of 11 is 1101 and has 3 set bits

1. Simple Method Loop through all bits in an integer, check if a bit is set and if it is then increment the set bit count. See below program.

Python3

# 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


# Program to test function countSetBits */
i = 9
print(countSetBits(i))

# This code is contributed by
# Smitha Dinesh Semwal

Output:

2

Recursive Approach :

Python3

# Python3 implementation of recursive
# approach to find the number of set
# bits in binary representation of
# positive integer n

def countSetBits( n):

    # base case
    if (n == 0):
        return 0

    else:

        # if last bit set add 1 else
        # add 0
        return (n & 1) + countSetBits(n >> 1)

# Get value from user
n = 9

# Function calling
print( countSetBits(n))

# This code is contributed by sunnysingh

Output:

2

Approach #3:Using bin method with number which return string which contains the binary representation of number and with count function of string we can count the set bit in number.

Python3

# Python3 implementation of built-in function
# approach to find the number of set
# bits in binary representation of
# positive integer n

def countSetBits( n):

    # Using bin function in number
    ans = bin( n )
    return ans.count( “ 1 ” )

# Get value from user
n = 9

# Function calling
print( countSetBits(n))

# This code is contributed by sam snehil

Output:

2

Please refer complete article on Count set bits in an integer for more details!