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.

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/**
* 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;
}
}