Update counting-bits.py

Author: kamyu104

Python/counting-bits.py

@@ -1,5 +1,5 @@
 # Time:  O(n)
-# Space: O(1)
+# Space: O(n)
 
 # Given a non negative integer number num. For every numbers i
 # in the range 0 <= i <= num calculate the number 
@@ -33,5 +33,6 @@ def countBits(self, num):
         """
         res = [0]
         for i in xrange(1, num + 1):
-            res.append(res[i >> 1] + (i & 1))
+            # Number of 1's in i = (i & 1) + number of 1's in (i / 2).
+            res.append((i & 1) + res[i >> 1])
         return res