class Solution {
    func countBits(num: Int) -> [Int] {
        var nums = [Int](count: num+1, repeatedValue: 0)
        if num == 0 { // if num is 0
            return nums
        }
        for i in 1...num {
            nums[i] = binaryOnes(i)
        }
        return nums
    }
    func binaryOnes(num: Int) -> Int {
        var num = num
        var count = 0
        repeat  {
            if num % 2 == 0 { // even numbers
                num /= 2
            } else { // all odd numbers
                num = (num-1)/2
                count += 1
            }
        } while num > 1
        if num == 1 { // when num is 1 at the end
            count += 1
        }
        return count
    }
}

repeat { ... } while num > 1

while num > 0 { ... }

func binaryOnes(num: Int) -> Int {
    var num = num
    var count = 0
    while num > 0 {
        if num % 2 == 0 { // even numbers
            num /= 2
        } else { // all odd numbers
            num = (num-1)/2
            count += 1
        }
    }
    return count
}

func binaryOnes(num: Int) -> Int {
    var num = num
    var count = 0
    while num > 0 {
        count += num % 2
        num /= 2
    }
    return count
}

func countBits(num: Int) -> [Int] {
    var nums = [Int](count: num+1, repeatedValue: 0)
    for i in 1...num {
        nums[i] = binaryOnes(i)
    }
    return nums
}

func countBits(upTo: Int) -> [Int] {
    return (0...upTo).map(binaryOnes)
}

bitCount(n) = bitCount(n/2) + (n % 2)

func countBits1(upTo: Int) -> [Int] {
    var result = [ 0 ]
    for i in 1...upTo {
        result.append(result[i/2] + (i % 2))
    }
    return result
}

func countBits(_ num: Int) -> [Int] {
    var ans = [Int]()

    for i in 0...num {
        ans.append(getOnes(x: i))
    }
    return ans
}

func getOnes(x: Int) -> Int {
    return String(x, radix: 2).filter {
        $0 == "1"
    }.count
}