LeetCode_OJ【24】Swap Nodes in Pairs

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.

这种题目是很基础的，但是还是得细心，最好在纸上给要操作的节点画出来。

/**
* 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) {
ListNode dummy = new ListNode(-1);
dummy.next = head;
ListNode pre = dummy;
while(pre.next!=null && pre.next.next != null){
ListNode cur1 = pre.next;
ListNode cur2 = cur1.next;
pre.next = cur2;
cur1.next = cur2.next;
cur2.next = cur1;
pre = cur1;
}
return dummy.next;
}
}