#链表 #两两交换链表中的节点

swap-nodes-in-pairs.cpp

/**
 * 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) {
        ListNode* dummy = new ListNode(0);
        dummy->next = head;

        ListNode* cur = dummy;
        while (cur->next != NULL && cur->next->next != NULL) {
            ListNode* node1 = cur->next; // 1
            ListNode* node2 = cur->next->next; // 2
            ListNode* node3 = cur->next->next->next; // 3
        
            cur->next = node2;
            cur->next->next = node1;
            cur->next->next->next = node3;

            cur = node1;
        }
        return dummy->next;
    }
};