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.
解题思路：
感觉和前几题很类似，直接实现即可，JAVA代码如下：
public ListNode swapPairs(ListNode head) {
ListNode result = new ListNode(0), index = result;
if (head == null)
return result.next;
while (head.next != null) {
index.next = new ListNode(head.next.val);
index = index.next;
index.next = new ListNode(head.val);
index = index.next;
head = head.next.next;
if (head == null)
return result.next;
}
index.next = new ListNode(head.val);
return result.next;
}