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 should use only constant space. You may?not?modify the values in the list, only nodes itself can be changed.
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/** * 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 first = null; ListNode second = head; ListNode third = head.next; while (third != null) { ListNode h = swap(second, third); if (first == null) { head = h; } else { first.next = h; } ListNode tmp = second; second = third; third = tmp; if (third.next == null) { return head; } else { first = third; second = second.next.next; third = third.next.next; } } return head; } private ListNode swap(ListNode second, ListNode third) { second.next = third.next; third.next = second; return third; } }
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原文:http://hcx2013.iteye.com/blog/2216804