diff --git a/src/algorithms/caching.py b/src/algorithms/caching.py
index 2adf488..7e6f05f 100644
--- a/src/algorithms/caching.py
+++ b/src/algorithms/caching.py
@@ -6,12 +6,16 @@ def time_based_cache(expiry_seconds: int) -> Callable:
     """Manual implementation of a time-based cache decorator."""
 
     def decorator(func: Callable) -> Callable:
-        cache: dict[str, tuple[Any, float]] = {}
+        cache: dict[tuple, tuple[Any, float]] = {}
+
+        def make_key(args, kwargs) -> tuple:
+            if kwargs:
+                items = tuple(sorted(kwargs.items()))
+                return (args, items)
+            return (args, None)
 
         def wrapper(*args, **kwargs) -> Any:
-            key_parts = [repr(arg) for arg in args]
-            key_parts.extend(f"{k}:{repr(v)}" for k, v in sorted(kwargs.items()))
-            key = ":".join(key_parts)
+            key = make_key(args, kwargs)
 
             current_time = time.time()