diff --git a/Sprint-2/improve_with_caches/fibonacci/fibonacci.py b/Sprint-2/improve_with_caches/fibonacci/fibonacci.py
index 60cc667..83f7a16 100644
--- a/Sprint-2/improve_with_caches/fibonacci/fibonacci.py
+++ b/Sprint-2/improve_with_caches/fibonacci/fibonacci.py
@@ -1,4 +1,15 @@
+cache = {}
+
+
 def fibonacci(n):
+    if n < 0:
+        raise ValueError("n must be non-negative  number")
+
     if n <= 1:
         return n
-    return fibonacci(n - 1) + fibonacci(n - 2)
+
+    if n in cache:
+        return cache[n]
+
+    cache[n] = fibonacci(n - 1) + fibonacci(n - 2)
+    return cache[n]
diff --git a/Sprint-2/improve_with_caches/making_change/making_change.py b/Sprint-2/improve_with_caches/making_change/making_change.py
index 255612e..16dd85e 100644
--- a/Sprint-2/improve_with_caches/making_change/making_change.py
+++ b/Sprint-2/improve_with_caches/making_change/making_change.py
@@ -7,13 +7,19 @@ def ways_to_make_change(total: int) -> int:
 
     For instance, there are two ways to make a value of 3: with 3x 1 coins, or with 1x 1 coin and 1x 2 coin.
     """
-    return ways_to_make_change_helper(total, [200, 100, 50, 20, 10, 5, 2, 1])
+    cache = {}
+    return ways_to_make_change_helper(total, [200, 100, 50, 20, 10, 5, 2, 1], cache)
 
 
-def ways_to_make_change_helper(total: int, coins: List[int]) -> int:
+def ways_to_make_change_helper(
+    total: int, coins: List[int], cache: dict[tuple, int]
+) -> int:
     """
     Helper function for ways_to_make_change to avoid exposing the coins parameter to callers.
     """
+    key = (total, tuple(coins))
+    if key in cache:
+        return cache[key]
     if total == 0 or len(coins) == 0:
         return 0
 
@@ -26,7 +32,11 @@ def ways_to_make_change_helper(total: int, coins: List[int]) -> int:
             if total_from_coins == total:
                 ways += 1
             else:
-                intermediate = ways_to_make_change_helper(total - total_from_coins, coins=coins[coin_index+1:])
+                intermediate = ways_to_make_change_helper(
+                    total - total_from_coins, coins=coins[coin_index + 1 :], cache=cache
+                )
                 ways += intermediate
             count_of_coin += 1
+
+    cache[key] = ways
     return ways