leetcode 338. Counting Bits

题目：

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) {
          if(num<0)
          {
              return null;
          }
          int[] binaryRepresentation=new int[num+1];
          for(int i=0;i<=num;i++)
          {
              int curNum=i;
              while(i>0)
              {
                  if((i&1)!=0)
                  {
                      binaryRepresentation[curNum]++;
                  }
                  i=i>>1;
              }
              i=curNum;
          }
          return binaryRepresentation; 
      }
  }