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

Author: kamyu104

C++/calculate-money-in-leetcode-bank.cpp

@@ -0,0 +1,18 @@
+// Time:  O(1)
+// Space: O(1)
+
+class Solution {
+public:
+    int totalMoney(int n) {
+        static const int cost = 1, day = 7;
+        static const auto arithmetic_sequence_sum =
+            [](int a, int d, int n) {
+                return (2 * a + (n - 1) * d) * n / 2;
+            };
+
+        int first_week_cost = arithmetic_sequence_sum(cost, cost, day);
+        int week = n / day, remain_day = n % day;
+        return arithmetic_sequence_sum(first_week_cost, cost * day, week) +
+               arithmetic_sequence_sum(cost * (week + 1), cost, remain_day);
+    }
+};