diff --git a/Sprint-2/improve_with_caches/fibonacci/fibonacci.py b/Sprint-2/improve_with_caches/fibonacci/fibonacci.py index 60cc667..7a9e8f7 100644 --- a/Sprint-2/improve_with_caches/fibonacci/fibonacci.py +++ b/Sprint-2/improve_with_caches/fibonacci/fibonacci.py @@ -1,4 +1,21 @@ -def fibonacci(n): - if n <= 1: - return n - return fibonacci(n - 1) + fibonacci(n - 2) +#def fibonacci(n): +# if n <= 1: +# return n +# return fibonacci(n - 1) + fibonacci(n - 2) +def fibonacci(n, cache=None): #cache dict is created only once to store results of previous calls. + if cache is None: + cache = {} + + if n in cache: #if n is already cached return it + return cache[n] + + if n <= 1: #If not cached, n <= 1, return base case (0 or 1) + cache[n] = n + else: + cache[n] = fibonacci(n - 1, cache) + fibonacci(n - 2, cache) #Cache the computed value for future reuse + + return cache[n]. #Return the cached or newly computed value. +#Time complexity of the function was O(2**n) and now using cache it becomes, +# O(n) since each fibonacci number from 0 - n is computed once +# Space Complexity O(n) +# i.e. Cache stores up to n results since recursion depth is n \ No newline at end of file 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..5496a71 100644 --- a/Sprint-2/improve_with_caches/making_change/making_change.py +++ b/Sprint-2/improve_with_caches/making_change/making_change.py @@ -1,32 +1,29 @@ 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. + coins = [200, 100, 50, 20, 10, 5, 2, 1] + cache = {} # To store already calculated results - 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]) + def count_ways(remaining, index): + # Base cases + if remaining == 0: + return 1 # Found a valid combination + if remaining < 0 or index == len(coins): + return 0 # Not possible + # Check cache + key = (remaining, index) + if key in cache: + return cache[key] + # Option 1: use current coin (stay on same index) + use_it = count_ways(remaining - coins[index], index) + # Option 2: skip current coin (move to next index) + skip_it = count_ways(remaining, index + 1) + # Store result in cache + cache[key] = use_it + skip_it + return cache[key] + return count_ways(total, 0) -def ways_to_make_change_helper(total: int, coins: List[int]) -> int: - """ - Helper function for ways_to_make_change to avoid exposing the coins parameter to callers. - """ - if total == 0 or len(coins) == 0: - 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 - return ways +#Time Complexity O(total × number of coins) +# Space Complexity O(total × number of coins) +#less expensive in relation to the original function