Top 50 Linked List Problems
Linked list problems test your ability to manipulate pointers and understand reference semantics. They are classic interview questions.
Essential Linked List Problems:
- Reverse a Linked List (iterative & recursive)
- Detect Cycle in a Linked List (Floyd's)
- Find Middle of Linked List (slow-fast)
- Merge Two Sorted Lists
- Merge K Sorted Lists
- Remove Nth Node From End
- Palindrome Linked List
- Linked List Cycle II (find cycle start)
- Intersection of Two Linked Lists
- Add Two Numbers (represented by lists)
- Sort List (merge sort on linked list)
- Reorder List
- Rotate List
- Copy List with Random Pointer
- LRU Cache (using doubly linked list + HashMap)
- Flatten a Multilevel Doubly Linked List
- Odd Even Linked List
- Swap Nodes in Pairs
- Reverse Nodes in k-Group
- Partition List
Strategies:
- Use dummy head to simplify edge cases.
- Slow-fast pointers for cycles and middle.
- Iterative reversal with three pointers.
- Recursion for some problems.
- Keep track of previous node.
Example: Reverse a Linked List (iterative)
public static ListNode reverseList(ListNode head) {
ListNode prev = null;
ListNode curr = head;
while (curr != null) {
ListNode next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
Two Minute Drill
- Linked lists require careful pointer management.
- Always consider edge cases: empty list, single node.
- Practice cycle detection, reversal, merging.
- Understand both iterative and recursive approaches.
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