From 23a434fb14424a4dbb61ea47c1a1b60ca5f6e902 Mon Sep 17 00:00:00 2001
From: mayank choudhary <mayanknst2028@gmail.com>
Date: Wed, 15 Oct 2025 22:53:12 +0530
Subject: [PATCH 1/2] feat: Implement LRU Cache algorithm

---
 data_structures/lru_cache.py | 88 ++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 data_structures/lru_cache.py

diff --git a/data_structures/lru_cache.py b/data_structures/lru_cache.py
new file mode 100644
index 000000000000..55f7f65b3927
--- /dev/null
+++ b/data_structures/lru_cache.py
@@ -0,0 +1,88 @@
+from __future__ import annotations
+
+class Node:
+    """A node in the doubly linked list."""
+    def __init__(self, key: int, val: int) -> None:
+        self.key, self.val = key, val
+        self.prev: Node | None = None
+        self.next: Node | None = None
+
+class LRUCache:
+    """
+    A Least Recently Used (LRU) Cache data structure.
+    >>> cache = LRUCache(2)
+    >>> cache.put(1, 1)
+    >>> cache.put(2, 2)
+    >>> cache.get(1)
+    1
+    >>> cache.put(3, 3)  # evicts key 2
+    >>> cache.get(2)
+    -1
+    >>> cache.put(4, 4)  # evicts key 1
+    >>> cache.get(1)
+    -1
+    >>> cache.get(3)
+    3
+    >>> cache.get(4)
+    4
+    """
+    def __init__(self, capacity: int) -> None:
+        if capacity <= 0:
+            raise ValueError("Capacity must be a positive integer.")
+        self.capacity = capacity
+        self.cache: dict[int, Node] = {}  # Maps key to node
+
+        self.head = Node(-1, -1)
+        self.tail = Node(-1, -1)
+        self.head.next = self.tail
+        self.tail.prev = self.head
+
+    def _remove(self, node: Node) -> None:
+        """Helper to remove a node from the list."""
+        if node.prev and node.next:
+            prev, nxt = node.prev, node.next
+            prev.next = nxt
+            nxt.prev = prev
+
+    def _add(self, node: Node) -> None:
+        """Helper to add a node to the front of the list (most recent)."""
+        if self.head.next:
+            node.prev = self.head
+            node.next = self.head.next
+            self.head.next.prev = node
+            self.head.next = node
+
+    def get(self, key: int) -> int:
+        if key in self.cache:
+            node = self.cache[key]
+            self._remove(node)
+            self._add(node)
+            return node.val
+        return -1
+
+    def put(self, key: int, value: int) -> None:
+        """
+        Adds or updates a key-value pair in the cache.
+        >>> cache = LRUCache(1)
+        >>> cache.put(1, 10)
+        >>> cache.get(1)
+        10
+        """
+        if key in self.cache:
+            node = self.cache[key]
+            node.val = value
+            self._remove(node)
+            self._add(node)
+        else:
+            new_node = Node(key, value)
+            self.cache[key] = new_node
+            self._add(new_node)
+
+            if len(self.cache) > self.capacity and self.tail.prev:
+                lru = self.tail.prev
+                self._remove(lru)
+                del self.cache[lru.key]
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()
\ No newline at end of file

From f5aac0e80356e1287389e6da095d2a296f3d95d4 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Thu, 16 Oct 2025 09:30:56 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 data_structures/lru_cache.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/data_structures/lru_cache.py b/data_structures/lru_cache.py
index 55f7f65b3927..585a02d2b8d2 100644
--- a/data_structures/lru_cache.py
+++ b/data_structures/lru_cache.py
@@ -1,12 +1,15 @@
 from __future__ import annotations
 
+
 class Node:
     """A node in the doubly linked list."""
+
     def __init__(self, key: int, val: int) -> None:
         self.key, self.val = key, val
         self.prev: Node | None = None
         self.next: Node | None = None
 
+
 class LRUCache:
     """
     A Least Recently Used (LRU) Cache data structure.
@@ -26,6 +29,7 @@ class LRUCache:
     >>> cache.get(4)
     4
     """
+
     def __init__(self, capacity: int) -> None:
         if capacity <= 0:
             raise ValueError("Capacity must be a positive integer.")
@@ -83,6 +87,8 @@ def put(self, key: int, value: int) -> None:
                 self._remove(lru)
                 del self.cache[lru.key]
 
+
 if __name__ == "__main__":
     import doctest
-    doctest.testmod()
\ No newline at end of file
+
+    doctest.testmod()