Python Program to Count set bits in an integer

Last Updated : 27 Jul, 2023

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

setbit

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

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:

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:

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 