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.

class Solution { int count(int n) { int cnt = 0; while (n != 0) { cnt += n % 2; n = n / 2; } return cnt; } public: vector<int> countBits(int num) { vector<int>re; int k = 0; while (k <= num) { re.push_back(count(k)); k++; } return re; } };

accepted