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WestMidlands| SDC NOV 2025 |Sara Tahir| Sprint 2 | Implement LRUCache #114
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,87 @@ | ||
| #Implementing a doubly linked list to reduce complexity of each operation which was previously O(n) to O(1). | ||
| class Node: | ||
| def __init__(self, key, value): | ||
| self.key = key | ||
| self.value = value | ||
| self.prev = None | ||
| self.next = None | ||
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| class DoublyLinkedList: | ||
| def __init__(self): | ||
| self.head = None # MRU | ||
| self.tail = None # LRU | ||
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| def push_head(self, node): #accessing or adding a new key at head- MRU | ||
| node.prev = None | ||
| node.next = self.head | ||
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| if self.head: | ||
| self.head.prev = node | ||
| self.head = node | ||
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| if self.tail is None: | ||
| self.tail = node | ||
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| def remove(self, node): | ||
| if node.prev: | ||
| node.prev.next = node.next #previous node connects to the next node. | ||
| else: | ||
| self.head = node.next | ||
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| if node.next: | ||
| node.next.prev = node.prev | ||
| else: | ||
| self.tail = node.prev | ||
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| node.prev = None | ||
| node.next = None | ||
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| def pop_tail(self): #removes to return lru node | ||
| if self.tail is None: | ||
| return None | ||
| node = self.tail | ||
| self.remove(node) | ||
| return node | ||
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| class LruCache: | ||
| def __init__(self,limit) -> None: | ||
| if limit <= 0: | ||
| raise ValueError("Limit must be greater than zero") | ||
| self.limit = limit #defines a limit, after which before adding anything in our cache we need to remove it | ||
| self.storage = {} #key(cachekey) and node(key value pair) | ||
| self.order = DoublyLinkedList() #self.head is MRU and self.tail is LRU | ||
| pass | ||
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| #If a key already exists move it to MRU position | ||
| def touch (self,node): | ||
| self.order.remove(node) | ||
| self.order.push_head(node) | ||
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| # If we want to add or update a key value pair | ||
| def set(self, key, value): | ||
| if key in self.storage: | ||
| node = self.storage[key] #update the value of the key | ||
| node.value = value | ||
| self.touch(node) | ||
| return | ||
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| #if we are adding a new key and at our limit | ||
| if len(self.storage) >= self.limit: | ||
| lru_node =self.order.pop_tail() | ||
| del self.storage[lru_node.key] | ||
|
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| #insert a new node | ||
| new_node = Node(key, value) | ||
| self.order.push_head(new_node) | ||
| self.storage[key] = new_node | ||
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| def get(self,key): | ||
| if key not in self.storage: | ||
| return None | ||
| node = self.storage[key] | ||
| self.touch(node) | ||
| return node.value | ||
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Could also use docstring to document the method.