https://shio-chan-dev.github.io/jeanblog/tags/two-pointers/Recent content in Two Pointers on Jeanphilo BlogHugo -- 0.159.2en-usThu, 12 Feb 2026 13:50:28 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/19-remove-nth-node-from-end-of-list/Thu, 12 Feb 2026 13:50:28 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/19-remove-nth-node-from-end-of-list/From naive two-pass traversal to one-pass fast/slow pointers, this ACERS guide explains Remove Nth Node From End of List with correctness intuition, edge cases, engineering mappings, and runnable multi-language code.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/142-linked-list-cycle-ii/Tue, 10 Feb 2026 10:47:56 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/142-linked-list-cycle-ii/Return the first node where a singly linked list enters a cycle without modifying the list: use Floyd fast/slow pointers to detect a meeting point, then reset one pointer to head and move both one step to localize the entry in O(n) time and O(1) space.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/21-merge-two-sorted-lists/Tue, 10 Feb 2026 10:47:02 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/21-merge-two-sorted-lists/Merge two sorted linked lists in O(m+n) with sentinel node and two pointers, with iterative and recursive comparison, engineering mapping, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/25-reverse-nodes-in-k-group/Tue, 10 Feb 2026 10:25:53 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/25-reverse-nodes-in-k-group/Reverse a linked list in groups of k nodes in-place, leaving the last group unchanged if its size is smaller than k. This guide presents a dummy-node + kth-scan + in-place reversal template in O(n) time and O(1) extra space.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/143-reorder-list/Tue, 10 Feb 2026 09:57:31 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/143-reorder-list/Reorder a linked list to L0->Ln->L1->Ln-1... in O(n) time and O(1) extra space using split, reverse, and alternating merge, with derivation, pitfalls, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/141-linked-list-cycle/Tue, 10 Feb 2026 08:55:58 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/141-linked-list-cycle/Detect whether a singly linked list has a cycle using Floyd fast/slow pointers in O(n) time and O(1) extra space, with proof intuition, pitfalls, engineering mapping, and runnable multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/160-intersection-of-two-linked-lists/Mon, 09 Feb 2026 09:26:37 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/160-intersection-of-two-linked-lists/Find the intersection node of two singly linked lists without modifying structure: two pointers switching heads synchronize in O(m+n) time and O(1) extra space, with derivation, engineering mapping, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/42-trapping-rain-water/Sat, 24 Jan 2026 10:40:53 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/hot100/42-trapping-rain-water/Compute trapped rain water in O(n) using two pointers and left/right maxima. Includes engineering scenarios, pitfalls, and multi-language implementations.https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1437-check-if-all-ones-are-at-least-k-places-away/Thu, 22 Jan 2026 10:49:42 +0800https://shio-chan-dev.github.io/jeanblog/alg/leetcode/1437-check-if-all-ones-are-at-least-k-places-away/One-pass check to ensure all 1s are at least k apart. Includes engineering scenarios, pitfalls, and multi-language implementations.