Hot100: Linked List Cycle II Floyd Detection + Entry Localization ACERS Guide
Subtitle / Summary LeetCode 142 upgrades cycle detection into cycle entry localization. The robust template is Floyd: first detect a meeting inside the cycle, then reset one pointer to head and move both by one step; the next meeting node is the cycle entry. Reading time: 12-16 min Tags: Hot100, linked list, fast slow pointers, Floyd SEO keywords: Linked List Cycle II, cycle entry, Floyd, fast slow pointers, O(1) space, LeetCode 142, Hot100 Meta description: Floyd cycle detection + entry localization with proof intuition, engineering mapping, and runnable multi-language implementations in O(n) time and O(1) extra space. Target Readers Hot100 learners who want to fully internalize the 141 -> 142 linked-list template family Developers who need to locate where a pointer chain becomes cyclic Interview candidates who want to explain why “reset to head” works Background / Motivation In real systems, cycle corruption in chain structures can cause: ...