反転チェーンテーブル-再帰実装leetcode 206

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(head==nullptr||head->next==nullptr){
            return head;
        }
       ListNode *save = reverse(head->next,head);
        head->next=nullptr;
        return save;
    }
    
    ListNode *reverse(ListNode *root, ListNode *last) {
    ListNode *n;
    if (root->next == nullptr) {
        root->next = last;
        return root;
    } else {
        n = reverse(root->next, last->next);
        root->next = last;
        return n;
    }
        return nullptr;
    }

};