Hot100: Merge Two Sorted Lists Sentinel Two-Pointer Merge ACERS Guide
Subtitle / Summary This problem is the linked-list version of merge-sort’s merge step. Use a sentinel node plus two pointers to splice nodes in ascending order in O(m+n), without rebuilding the list. Reading time: 10-12 min Tags: Hot100, linked list, merge, two pointers SEO keywords: Merge Two Sorted Lists, sentinel node, linked list merge, LeetCode 21, Hot100 Meta description: A complete ACERS guide for LeetCode 21 with derivation, correctness invariants, pitfalls, and runnable multi-language code. Target Readers Hot100 learners preparing linked-list interview templates Developers who often lose nodes while rewiring next Engineers who need stable O(1)-extra-space merge patterns Background / Motivation This is a small problem with large transfer value: ...