countingBits.java

// 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.

public class Solution {

    public int[] countBits(int num) {
        
        int[] bits = new int[num + 1];
        
        bits[0] = 0;
        
        for(int i = 1; i <= num; i++) {
            
            bits[i] = bits[i >> 1] + (i & 1);
            
        }
        
        return bits;
        
    }

}