LeetCode 24 JAVA

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        ListNode fakeHead = new ListNode(0);
        fakeHead.next = head;
        ListNode pre = fakeHead;
        ListNode ptr = pre.next;
        while(ptr != null && ptr.next != null){
            ListNode temp = ptr.next;
            ListNode next = temp.next;
            pre.next = temp;
            temp.next = ptr;
            ptr.next = next;
            
            pre = ptr;
            ptr = next;
        }
        pre.next = ptr;
        return fakeHead.next;
    }
}

　　画图理解。