Linked List Problems and Tricks

Dummy Node Trick

Use a dummy head so you don't need special cases for the first node when building a new list (e.g. merge two lists, remove elements).

Reversal

• Iterative: Three pointers (prev, curr, next); reverse links one by one.
• Recursive: Reverse rest, then link current to the new tail.

Cycle Detection

Floyd's algorithm: Slow and fast pointer; if they meet, there's a cycle. To find cycle start: reset slow to head, move both one step at a time until they meet.

Merging and Splitting

• Merge two sorted lists: dummy node, compare and attach.
• Merge K sorted lists: min-heap of size K.
• Split: traverse with two pointers or count nodes first.

Other Classic Problems

• Remove Nth node from end: two pointers, gap N.
• Palindrome: find middle, reverse second half, compare.
• Reorder list: find middle, reverse, merge two halves.

Summary

Dummy node, reversal, and fast-slow pointer cover most list problems. Practice on Preplume(/) to build speed.