| | | 1 | | // -------------------------------------------------------------------------------- |
| | | 2 | | // Copyright (C) 2025 Eugene Eremeev (also known as Yevhenii Yeriemeieiv). |
| | | 3 | | // All Rights Reserved. |
| | | 4 | | // -------------------------------------------------------------------------------- |
| | | 5 | | // This software is the confidential and proprietary information of Eugene Eremeev |
| | | 6 | | // (also known as Yevhenii Yeriemeieiv) ("Confidential Information"). You shall not |
| | | 7 | | // disclose such Confidential Information and shall use it only in accordance with |
| | | 8 | | // the terms of the license agreement you entered into with Eugene Eremeev (also |
| | | 9 | | // known as Yevhenii Yeriemeieiv). |
| | | 10 | | // -------------------------------------------------------------------------------- |
| | | 11 | | |
| | | 12 | | using LeetCode.Core.Models; |
| | | 13 | | |
| | | 14 | | namespace LeetCode.Algorithms.PalindromeLinkedList; |
| | | 15 | | |
| | | 16 | | /// <inheritdoc /> |
| | | 17 | | public class PalindromeLinkedListSlowFastPointers : IPalindromeLinkedList |
| | | 18 | | { |
| | | 19 | | /// <summary> |
| | | 20 | | /// Time complexity - O(n) |
| | | 21 | | /// Space complexity - O(1) |
| | | 22 | | /// </summary> |
| | | 23 | | /// <param name="head"></param> |
| | | 24 | | /// <returns></returns> |
| | | 25 | | public bool IsPalindrome(ListNode? head) |
| | 13 | 26 | | { |
| | 13 | 27 | | if (head?.next == null) |
| | 1 | 28 | | { |
| | 1 | 29 | | return true; |
| | | 30 | | } |
| | | 31 | | |
| | 12 | 32 | | var slow = head; |
| | 12 | 33 | | var fast = head; |
| | | 34 | | |
| | 27 | 35 | | while (fast.next is { next: not null }) |
| | 15 | 36 | | { |
| | 15 | 37 | | slow = slow?.next; |
| | 15 | 38 | | fast = fast.next.next; |
| | 15 | 39 | | } |
| | | 40 | | |
| | | 41 | | |
| | 12 | 42 | | var secondHalfStart = ReverseList(slow?.next); |
| | | 43 | | |
| | 12 | 44 | | var firstHalfStart = head; |
| | | 45 | | |
| | 28 | 46 | | while (secondHalfStart != null) |
| | 20 | 47 | | { |
| | 20 | 48 | | if (firstHalfStart != null && firstHalfStart.val != secondHalfStart.val) |
| | 4 | 49 | | { |
| | 4 | 50 | | return false; |
| | | 51 | | } |
| | | 52 | | |
| | 16 | 53 | | firstHalfStart = firstHalfStart?.next; |
| | 16 | 54 | | secondHalfStart = secondHalfStart.next; |
| | 16 | 55 | | } |
| | | 56 | | |
| | 8 | 57 | | return true; |
| | 13 | 58 | | } |
| | | 59 | | |
| | | 60 | | private static ListNode? ReverseList(ListNode? head) |
| | 12 | 61 | | { |
| | 12 | 62 | | ListNode? reverseHead = null; |
| | | 63 | | |
| | 35 | 64 | | while (head != null) |
| | 23 | 65 | | { |
| | 23 | 66 | | var nextTemp = head.next; |
| | 23 | 67 | | head.next = reverseHead; |
| | 23 | 68 | | reverseHead = head; |
| | 23 | 69 | | head = nextTemp; |
| | 23 | 70 | | } |
| | | 71 | | |
| | 12 | 72 | | return reverseHead; |
| | 12 | 73 | | } |
| | | 74 | | } |