338. Counting Bits

    func countBits(_ num: Int) -> [Int] {
        guard num > 0 else { return [0] }
        var dp = [Int](repeating: 0, count: num + 1)
        dp[1] = 1
        dp[0] = 0
        for i in  stride(from: 2, through: num, by: 1){
            dp[i] = i % 2 + dp[i / 2]
        }
        return dp
    }