LeetCode-in-All

338. Counting Bits

Easy

Given an integer n, return an array ans of length n + 1 such that for each i (0 <= i <= n), ans[i] is the number of 1’s in the binary representation of i.

Example 1:

Input: n = 2

Output: [0,1,1]

Explanation:

0 --> 0
1 --> 1
2 --> 10 

Example 2:

Input: n = 5

Output: [0,1,1,2,1,2]

Explanation:

0 --> 0
1 --> 1
2 --> 10
3 --> 11
4 --> 100
5 --> 101 

Constraints:

Follow up:

Solution

class Solution {
    func countBits(_ n: Int) -> [Int] {
        var result = [Int]()

        for num in 0 ... n {
            var count = 0
            var curr = num
            
            while curr > 0 {
                count += curr & 1
                curr = curr >> 1
            }
            result.append(count)
        }
        return result
    }
}