Linked List Patterns
Linked lists are a fundamental data structure, and many coding interview problems center around common patterns in linked list manipulation. Here we organize key patterns for solving linked list problems and how to recognize them. From basic operations to advanced techniques (two-pointer approaches, in-place reversal, partitioning, merging, using extra pointers, etc.), this summary covers the major approaches. It includes examples from LeetCode (and similar platforms) with Java solutions and explanations for each pattern. This should serve as a comprehensive revision resource for linked list problems.
This covers the basics of singly and doubly linked lists, including traversal and modifications at various positions (head, tail, middle). It also touches on circular linked lists (which connect the tail back to the head) and even skip lists. The core idea is understanding pointer manipulation: to insert or delete a node, you typically keep track of the current node and its previous node. Special techniques like using a dummy (sentinel) node are often employed to simplify edge cases at the head or tail:. In a doubly linked list, having a
prev pointer makes deletions easier (you can remove a node in O(1) if you have a direct reference). For circular linked lists, remember that the traversal must stop when you reach the starting point again (to avoid infinite loops).Example Problems:
Design Linked List (LeetCode 707)Remove Linked List Elements (LeetCode 203)Insert into a Sorted Circular Linked List (LeetCode 708)
Solution Spotlight: Remove Linked List Elements (LeetCode 203)
We create a dummy head node that points to the start of the list to simplify deletion logic (particularly for cases where the head node itself needs to be removed):. Then we iterate through the list with a pointer
current. If current.next has the target value, we bypass that node by pointing current.next to current.next.next, effectively removing it. Otherwise, we simply move current forward. Using the dummy node ensures that even if the original head contains the value to be removed, our loop can handle it uniformly. The result is returned via dummy.next (which will be the updated head of the list). This runs in O(n) time with O(1) extra space.RemoveLinkedListElements(LeetCode203).java
Loading code syntax...