refactor: use memoisation to avoid recalulations

Author: JanefrancessC

Sprint-2/improve_with_caches/fibonacci/fibonacci.py

@@ -1,12 +1,10 @@
-_cache = {}
-
-def fibonacci(n):
-    if n in _cache:
-        return _cache[n]
+def fibonacci(n, cache={}):
+    if n in cache:
+        return cache[n]
 
     if n <= 1:
         return n
 
     result = fibonacci(n - 1) + fibonacci(n - 2)
-    _cache[n] = result
+    cache[n] = result
     return result

Sprint-2/improve_with_caches/making_change/making_change.py

@@ -1,32 +1,35 @@
-from typing import List
-
-
 def ways_to_make_change(total: int) -> int:
     """
     Given access to coins with the values 1, 2, 5, 10, 20, 50, 100, 200, returns a count of all of the ways to make the passed total value.
 
     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])
+    return ways_to_make_change_helper(total, 0)
 
 
-def ways_to_make_change_helper(total: int, coins: List[int]) -> int:
+def ways_to_make_change_helper(total: int, coin_index: int, cache={}) -> int:
     """
     Helper function for ways_to_make_change to avoid exposing the coins parameter to callers.
     """
-    if total == 0 or len(coins) == 0:
+    coins = (200, 100, 50, 20, 10, 5, 2, 1)
+
+    key = (total, coin_index)
+
+    if key in cache:
+        return cache[key]
+
+    if total == 0:
+        return 1
+    
+    if coin_index == len(coins):
         return 0
 
-    ways = 0
-    for coin_index in range(len(coins)):
-        coin = coins[coin_index]
-        count_of_coin = 1
-        while coin * count_of_coin <= total:
-            total_from_coins = coin * count_of_coin
-            if total_from_coins == total:
-                ways += 1
-            else:
-                intermediate = ways_to_make_change_helper(total - total_from_coins, coins=coins[coin_index+1:])
-                ways += intermediate
-            count_of_coin += 1
+    coin = coins[coin_index]
+
+    if coin > total:
+        ways = ways_to_make_change_helper(total, coin_index + 1)
+    else:
+        ways = (ways_to_make_change_helper(total - coin, coin_index) + ways_to_make_change_helper(total, coin_index + 1))
+
+    cache[key] = ways
     return ways