Leetcode24. 两两交换链表中的节点

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        //哨兵节点
        ListNode * PreHead = new ListNode(0);
        
        PreHead->next = head;
        //指向哨兵节点
        ListNode * temp = PreHead;
        
        while(temp->next != nullptr && temp->next->next != nullptr){
            ListNode * node1 = temp->next;
            ListNode * node2 = temp->next->next;
            temp->next = node2;
            node1->next = node2->next;
            node2->next = node1;
            temp = node1;
        }
        return PreHead->next;

    }
};