We’re solving another LeetCode problem today instead of adding a new project to my portfolio. This one is focused on bit manipulation. Let’s dive in.

The Problem

Today’s problem is 191. Number of 1 Bits. The problem is as follows: Write a function that takes the binary representation of a positive integer and returns the number of set bits it has (also known as the Hamming weight).

The Solution

Let’s answer using the UMPIRE method:

  • Understand
    • We are given a positive integer, and we are to count the number of 1 bits of the number in bina.
  • Match
    • We can match this problem to a bit manipulation problem or an array looping problem.
  • Plan
    • We can write a function which casts the number to binary, then a string, and finally counts the number of 1’s using a loop.
  • Implement
    def countBits(self, n: int) -> int:
        b = bin(n)
        s = str(b)[2:]
        count = 0
        for bit in s:
            if bit == '1':
                count += 1
        return count
  • Review
    • The code is clean and concise. We used descriptive variable names.
    • We can test our code using the examples provided.
    • n = 4
      • b = ‘0b0100’
      • s = ‘0100’
      • count = 1
    def test_reverseBits(self):
        assert self.countBits(4) == 1
        assert self.reverseBits(3) == 2
  • Evaluate
    • Our code runs in O(n) time complexity due to our loop through the string.
    • Our space complexity is O(1) as we use the same amount of space regardless of input size.