Created
January 12, 2026 02:54
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Cool Linked List
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| class Node: | |
| def __init__(self, val: int, next = None, prev = None): | |
| self.val = val | |
| self.next = next | |
| self.prev = prev | |
| class LinkedList: | |
| def __init__(self): | |
| self.size = 0 | |
| self.sentinel = Node(0) | |
| self.sentinel.next = self.sentinel | |
| self.sentinel.prev = self.sentinel | |
| def get(self, index: int) -> int: | |
| if index < 0 or index >= self.size: | |
| return - 1 | |
| node = self._get_node(index) | |
| return node.val | |
| def addAtHead(self, val: int) -> None: | |
| self._insert_after(self.sentinel, val) | |
| def addAtTail(self, val: int) -> None: | |
| self._insert_after(self.sentinel.prev, val) | |
| def addAtIndex(self, index: int, val: int) -> None: | |
| if index < 0: | |
| index = 0 | |
| if index > self.size: | |
| return | |
| prev = self.sentinel if index == 0 else self._get_node(index - 1) | |
| self._insert_after(prev, val) | |
| def deleteAtIndex(self, index: int) -> None: | |
| if index < 0 or index >= self.size: | |
| return | |
| node = self._get_node(index) | |
| self._remove(node) | |
| def _remove(self, node: Node): | |
| node.prev.next = node.next | |
| node.next.prev = node.prev | |
| self.size -= 1 | |
| def _insert_after(self, prev: Node, val: int) -> None: | |
| node = Node(val, prev.next, prev) | |
| prev.next.prev = node | |
| prev.next = node | |
| self.size += 1 | |
| def _get_node(self, index: int): | |
| curr = self.sentinel | |
| if index < self.size // 2: | |
| for _ in range(index + 1): | |
| curr = curr.next | |
| else: | |
| for _ in range(self.size - index): | |
| curr = curr.prev | |
| return curr |
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