LeetCode solution Report-Swap Nodes in Pairs

LeetCode solution Report-Swap Nodes in Pairs

Question:

Given a linked list, swap every two adjacent nodes and return its head.
For example,
Given 1-> 2-> 3-> 4, you should return the list as 2-> 1-> 4-> 3.
Your algorithm shocould use only constant space. You may not modify the values in the list, only nodes itself can be changed.
Original question: https://leetcode.com/problems/swap-nodes-in-pairs/

Analysis: the meaning of the question requires that the given linked list, adjacent nodes, be switched to the location, and return the changed linked list.
The basic idea is to use the pointer shift method. Pay attention to special cases, such as the empty linked list, the length of the linked list is 0, 1, and 2.
The following figure shows the concept:

Different colors indicate different cycles. <喎?http: www.bkjia.com kf ware vc " target="_blank" class="keylink"> VcD4NCjxwPmphdmG0 + slriefjy2vwdgvkow.vcd4ncjxwcmugy2xhc3m9 "brush: java;"> /** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */public class Solution { public ListNode swapPairs(ListNode head) { if (head == null || head.next == null) { return head; } ListNode p; ListNode q; ListNode k; p = head; q = p.next; k = q.next; head = head.next; while (q != null) { q.next = p; if(k != null && k.next != null){ p.next = k.next; p = k; q = k.next; k = k.next.next; }else{ p.next = k; q = null; k = null; } /*p = k; if(k != null){ q = k.next; }else{ q = null; } if(k != null && k.next != null){ k = k.next.next; }else{ k = null; }*/ } return head; }}