[swift] LeetCode 338. Counting Bits

Given a non negative integer number num. For every numbers i in the range 0 ≤ i ≤ num calculate the number of 1’s in their binary representation and return them as an array.

Example:

For num = 5 you should return [0,1,1,2,1,2].

Follow up:

It is very easy to come up with a solution with run time O(n*sizeof(integer)). But can you do it in linear time O(n) /possibly in a single pass?

Space complexity should be O(n).

Can you do it like a boss? Do it without using any builtin function like __builtin_popcount in c++ or in any other language.

func countBits(_ num: Int) -> [Int] {
    var arr = Array(repeating: 0, count: num+1), i = 0
    while i <= num {
        arr[i] = i.nonzeroBitCount
        i += 1
    }
 
    return arr
}

（随着网站访问量的激增，服务器配置只得一再升级以维持网站不“404 Not Found”，所以网站的维护费用也在不断上涨……（目前的阿里云服务器ECS+云数据库RDS+域名购买+七牛云的费用是2200元/年），为了能不放弃该网站，所以我又把打赏链接放上来啦～所有打赏金额都会被记账并投入博客维护中，感谢厚爱，多多关照～）