LeetCode: 338 solved

Author: devMEremenko

Python/LeetCode/338. Counting Bits.py

@@ -0,0 +1,24 @@
+# https://leetcode.com/problems/counting-bits/
+
+class Solution:
+    def countBits(self, num: int) -> [int]:
+        # return self.solution1(num)
+        return self.solution2(num)
+    
+    # Time: O(n * sizeOf(int))
+    def solution1(self, num):
+        return list(map(lambda i: bin(i).count("1"), range(0, num + 1)))
+    
+    # Time: O(n)
+    # even: countBits(i) == countBits(i // 2)
+    # odd:  countBits(i) == countBits(i - 1) + 1 where (i - 1) is even
+    # 2: 00010
+    # 4: 00100
+    # 8: 01000
+    def solution2(self, num):
+        res = [0] * (num + 1)
+        for i in range(num + 1):
+            #         or i >> 1  or i % 2
+            res[i] = res[i // 2] + (i & 1)
+        return res
+