反转链表整个链表以及部分链表（递归）

#include 

struct ListNode
{
    int val;
    struct ListNode *next;
    ListNode(int x) : val(x), next(nullptr)
    {
    }
};

class Solution
{
public:
    //以head为起点，反转链表，并返回头节点
    ListNode *ReverseList(ListNode *pHead)
    {
        if (pHead == nullptr || pHead->next == nullptr)
        {
            return nullptr;
        }

        ListNode *last = ReverseList(pHead->next);
        pHead->next->next = pHead;
        pHead->next = pHead;
        return last;
    }
};

#反转链表的前N个结点

#include 

struct ListNode
{
    int val;
    struct ListNode *next;
    ListNode(int x) : val(x), next(nullptr)
    {
    }
};

class Solution
{
public:
    ListNode *rearNode = nullptr;
    ListNode *ReverseListN(ListNode *pHead, int n)
    {
        //记录n+1结点
        if (n == 1)
        {
            rearNode = pHead->next;
            return pHead;
        }

        ListNode *last = ReverseListN(pHead->next, n - 1);
        pHead->next->next = pHead;
        pHead->next = rearNode;
        return last;
    }
};

#include 

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 *rearNode = nullptr;
    ListNode *ReverseListN(ListNode *pHead, int n)
    {
        if (n == 1)
        {
            rearNode = pHead->next;
            return pHead;
        }

        ListNode *last = ReverseListN(pHead->next, n - 1);
        pHead->next->next = pHead;
        pHead->next = rearNode;
        return last;
    }

    ListNode *reverseBetween(ListNode *head, int left, int right)
    {
        if (left == 1)
        {
            return ReverseListN(head, right);
        }
        head->next = reverseBetween(head->next, left - 1, right - 1);
        return head;
    }
};