24. Swap Nodes in Pairs

image.png

一定要用好dummy节点，当head节点改变的时候，别忘了可以用dummy节点

/**
 * 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 == NULL){
            return head;
        }
        ListNode *dummy = new ListNode(0);
        dummy->next = head;
        ListNode *prev = dummy, *cur = head;
        while(cur && cur->next){
            ListNode *tmp = cur->next->next;
            prev->next = cur->next;
            cur->next->next = cur;
            cur->next = tmp;
            prev = cur;
            cur = tmp;
        }
        return dummy->next;
        
    }
};