LeetCode | Swap Nodes in Pairs

https://leetcode.com/problems/swap-nodes-in-pairs/

链表的操作题，往往画个图，逻辑就很清晰了。

C++

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if (!head || !head->next) return head;
        
        ListNode dummy(0); dummy.next = head;
        ListNode *pre1 = &dummy, *ptr1 = head, *ptr2 = head->next;
        while (ptr1 && ptr2) {
            ptr1->next = ptr1->next->next;
            ptr2->next = ptr1;
            pre1->next = ptr2;
            
            pre1 = ptr1;
            ptr1 = pre1->next;
            if (ptr1) ptr2 = ptr1->next;
            else ptr2 = NULL;
        }
        
        return dummy.next;
    }
};