MAY-28 2020 Challenge

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 in Java :

class Solution{
public int[] countBits(int num) {
    int[] result = new int[num+1];

    for(int i=0; i<=num; i++){
        result[i] = countEach(i);
    }

    return result;
}

public int countEach(int num){
    int result = 0;

    while(num!=0){
        if(num%2==1){
            result++;
        }
        num = num/2;
    }

    return result;
}
}