Create count-integers-with-even-digit-sum.py

Author: kamyu104

Python/count-integers-with-even-digit-sum.py

@@ -0,0 +1,49 @@
+# Time:  O(logn)
+# Space: O(1)
+
+# math
+class Solution(object):
+    def countEven(self, num):
+        """
+        :type num: int
+        :rtype: int
+        """
+        def parity(x):
+            result = 0
+            while x:
+                result += x%10
+                x //= 10
+            return result%2
+
+        return (num-parity(num))//2
+
+
+# Time:  O(nlogn)
+# Space: O(1)
+# brute force
+class Solution2(object):
+    def countEven(self, num):
+        """
+        :type num: int
+        :rtype: int
+        """
+        def parity(x):
+            result = 0
+            while x:
+                result += x%10
+                x //= 10
+            return result%2
+
+        return sum(parity(x) == 0 for x in xrange(1, num+1))
+
+
+# Time:  O(nlogn)
+# Space: O(logn)
+# brute force
+class Solution3(object):
+    def countEven(self, num):
+        """
+        :type num: int
+        :rtype: int
+        """
+        return sum(sum(map(int, str(x)))%2 == 0 for x in xrange(1, num+1))