Counting Bits

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.

Solutions

🧠 Cpp

class Solution
{
public:
    vector<int> countBits(int num)
    {
        vector<int> res(num+1);

        for(int i = 0; i <= num; ++i)
            res[i] = __builtin_popcount(i);

        return res;
    }
};