Create digit-count-in-range.py

Python/digit-count-in-range.py

@@ -0,0 +1,22 @@
+# Time:  O(logn)
+# Space: O(1)
+
+class Solution(object):
+    def digitsCount(self, d, low, high):
+        """
+        :type d: int
+        :type low: int
+        :type high: int
+        :rtype: int
+        """
+        def digitsCount(n, k):
+            pivot, result = 1, 0
+            while n >= pivot:
+                result += (n//(10*pivot))*pivot + \
+                           min(pivot, max(n%(10*pivot) - k*pivot + 1, 0))
+                if k == 0:
+                    result -= pivot
+                pivot *= 10
+            return result+1
+
+        return digitsCount(high, d) - digitsCount(low-1, d)