24. 两两交换链表中的节点/C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if(!head || !head->next) return head;
        
 
        ListNode* node1 = head;
        ListNode* node2 = head->next;
        node1->next = node2->next;
        node2->next = node1;
        head = node2;
        
        node1 = head->next;
        node2 = node1->next;
        while(node2 && node2->next){
            ListNode* node3 = node2->next->next;
            node1->next = node2->next;
            node1->next->next = node2;
            node2->next = node3;
            
            node1 = node2;
            node2 = node1->next;
        }
        return head;
    }
};