力扣刷题 24.两两交换链表中的节点--day4

题目分析

还是那句话， 需要先模拟一下节点交换的过程
将整个过程细分为一个个小过程，以此类推下去
注意画图分析

设置三个指针 post cur pre
注意 1. 节点的交换过程 2. 指针的递推

解法

ListNode *swapPairs(ListNode *head)
{
    if (!head)
        return nullptr;
    ListNode *dummyHead = new ListNode();
    dummyHead->next = head;
    ListNode *post = dummyHead, *cur = head, *pre = head->next;

    while (cur && pre)
    {
        ListNode *temp = pre->next;
        pre->next = cur;
        cur->next = temp;
        post->next = pre;

        post = cur;
        cur = cur->next;
        if (cur == nullptr)
        {
            pre = nullptr;
        }
        else
        {
            pre = cur->next;
        }
    }
    head = dummyHead->next;
    delete dummyHead;
    return head;
}