Create calculate-money-in-leetcode-bank.py

Author: kamyu104

Python/calculate-money-in-leetcode-bank.py

@@ -0,0 +1,17 @@
+# Time:  O(1)
+# Space: O(1)
+
+class Solution(object):
+    def totalMoney(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        def arithmetic_sequence_sum(a, d, n):
+            return (2*a + (n-1)*d) * n //2
+
+        cost, day = 1, 7
+        first_week_cost = arithmetic_sequence_sum(cost, cost, day)
+        week, remain_day = divmod(n, day)
+        return arithmetic_sequence_sum(first_week_cost, cost*day, week) + \
+               arithmetic_sequence_sum(cost*(week+1), cost, remain_day)