338. Counting Bits.cpp

#MayChallenge
/*
Link: https://leetcode.com/problems/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.
*/


// Solution

class Solution {
public:
    vector<int> countBits(int num) {
        vector<int> ans(num + 1, 0);
        
        for(int i = 0; i <= num; i++) {
            ans[i] = (i & 1) ? ans[i - 1] + 1 : ans[i>>1];
        }
        
        return ans;
    }
};