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 1:

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

Example 2:

Input: 5
Output:[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.

# @lc code=start
using LeetCode

function count_bits(num::Int)
    res = fill(1, num)
    for i in 2:num
        res[i] = res[i >> 1] + (i & 1)
    end
    pushfirst!(res, 0)
end
# @lc code=end

count_bits (generic function with 1 method)

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