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. A - Algorithm (Problem and Algorithm) Problem Restatement Given heads list1 and list2 of two sorted linked lists, merge them into one sorted linked list and return its head. The merged list should be formed by splicing together nodes from the original lists. ...