Swap Nodes in Pairs

目录

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. 

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode swapPairs(ListNode head) {
        ListNode c = null;
        ListNode n = null;
        ListNode nn = null;
        if(head==null){
            return null;
        }
        if(head.next!=null){
        	nn = head.next;
    	}else{
    	    return head;
    	}

        c = head;
        while(true){
        	if(c.next!=null){
        		n = c.next.next;
        		c.next.next=c;
        		if(n==null){
        		    c.next=n;
        		}else if(n.next!=null){
        			c.next=n.next;
        			c = n;
        			continue;
        		}else{
        			c.next=n;
        		}
        		if(c.next==null)break;
        		c = c.next;
        	}else{
        		break;
        	}
        }
        return nn;
    }
}
LeetCode
LeetCode