LeetCode24-Swap-Nodes-in-Pairs

Given a linked list, swap every two adjacent nodes and return its
head.

You may not modify the values in the list's nodes, only nodes itself
may be changed.

Example:

Given 1->2->3->4, you should return the list as 2->1->4->3.

public ListNode swapPairs(ListNode head) {    ListNode trueHead=new ListNode(0);    trueHead.next=head;    ListNode cur=trueHead;    while(cur.next!=null && cur.next.next!=null){        ListNode first=cur.next;        ListNode second=cur.next.next;        cur.next=second;        first.next=second.next;        second.next=first;        cur=first;     }    return trueHead.next;}