Python Count set bits in a range?
A given positive number when converted to binary, has a number of setbits. Set bits in a binary number is represented by 1. In this article we will see how to get the number of setbits in a given number after it is converted to binary value.
Using bin and slicing
In the below example we take a number and apply the bin function to get the binary value. Then we slice it to remove the prefixes added to a binary number and then apply the range function to get the coutn of setbits.
Example
Live Demo
def SetBits_cnt(n, l, r):
bin_val = bin(n)
# Remove '0b' prefixed in bin_val conversion
bin_val = bin_val[2:]
print(bin_val)
# reverse string
bin_val = bin_val[-1::-1]
# count all set bit '1' starting from index l-1
print(len([bin_val[i] for i in range(l - 1, r) if bin_val[i] == '1']))
SetBits_cnt(83,1,6)
Output
Running the above code gives us the following result −
1010011
3
Using bitwise
The bitwise operator can also be used to get the setbits. In the below example we first apply the bitwise operator taking the range into consideration and then pass it on to another function which counts only the set bits.
Example
Live Demo
def trackBitsInRange(n, l, r):
# using bitwise operator
bit_num = ((1 << r) - 1) ^ ((1 << (l - 1)) - 1)
# After bitwise operation count the set bits
return trackSetBits(n & bit_num)
def trackSetBits(n):
count = 0
while (n):
n &= (n - 1)
count = count + 1
return count
print(trackBitsInRange(83,1,6))
Output
Running the above code gives us the following result −
3
Published on 12-Jan-2021 13:30:34
