problems(cpp): add “1716. Calculate Money in Leetcode Bank”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/cpp/calculate-money-in-leetcode-bank.cpp

@@ -0,0 +1,15 @@
+class Solution {
+public:
+    int totalMoney(int n) {
+        auto monday = 1;
+
+        int total = 0;
+        for (; n >= 7; ++monday, n -= 7) {
+            total += 7 * (2 * monday + 7 - 1) / 2;
+        }
+
+        total += n * (monday + monday + n - 1) / 2;
+
+        return total;
+    }
+};