leetcode 24. 两两交换链表中的节点

题目描述

代码

/*** 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) {if(head==nullptr || head->next == nullptr)return head;ListNode *dummyHead = new ListNode(-1,head);ListNode *pre = dummyHead;ListNode *newHead = nullptr;ListNode *post;while(pre->next != nullptr && pre->next->next != nullptr){ListNode *pair1 = pre->next;ListNode *pair2 = pre->next->next;if(newHead == nullptr)newHead = pair2;post = pair2->next;pair2->next = pair1;pair1->next = post;pre->next = pair2;pre = pair1;}delete dummyHead;dummyHead = nullptr;return newHead;}
};