CODE-0003 · claude-haiku-4-5 (high)Perfect. The implementation is correct and handles all edge cases. Here is the solution:
```python
class LRUCache:
"""A least-recently-used cache with O(1) average-time get and put operations."""
def __init__(self, capacity):
"""Initialize cache with given capacity (non-negative integer)."""
self.capacity = capacity
self.cache = {} # key -> Node
self.head = Node(0, 0) # dummy head node
self.tail = Node(0, 0) # dummy tail node
self.head.next = self.tail
self.tail.prev = self.head
def get(self, key):
"""
Return value for key, or -1 if not present.
A successful get marks the key as most recently used.
"""
if key not in self.cache:
return -1
node = self.cache[key]
self._move_to_front(node)
return node.value
def put(self, key, value):
"""
Insert or update value for key, marking it as most recently used.
If cache exceeds capacity, evict the least recently used key.
"""
if self.capacity == 0:
return
if key in self.cache:
# Update existing key and move to front
node = self.cache[key]
node.value = value
self._move_to_front(node)
else:
# Add new key
node = Node(key, value)
self.cache[key] = node
self._add_to_front(node)
# Evict LRU if necessary
if len(self.cache) > self.capacity:
lru_node = self.tail.prev
self._remove_node(lru_node)
del self.cache[lru_node.key]
def _move_to_front(self, node):
"""Remove node from its current position and add it to the front."""
self._remove_node(node)
self._add_to_front(node)
def _add_to_front(self, node):
"""Add node right after the dummy head (most recently used position)."""
node.prev = self.head
node.next = self.head.next
self.head.next.prev = node
self.head.next = node
def _remove_node(self, node):
"""Remove node from its current position in the linked list."""
node.prev.next = node.next
node.next.prev = node.prev
class Node:
"""A node in the doubly-linked list used for LRU ordering."""
def __init__(self, key, value):
self.key = key
self.value = value
self.prev = None
self.next = None
```