题解 | #链表内指定区间反转#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @param m int整型 
     * @param n int整型 
     * @return ListNode类
     */
    ListNode *successor = nullptr; // 后驱节点
    ListNode* reverseN(ListNode* head, int n) {
        // write code here
        if ( n == 1) {
            successor = head->next;
            return head;
        }
        ListNode *last = reverseN(head->next , n-1);
        head->next->next = head;
        head->next = successor;
        return last;
    }

    ListNode* reverseBetween(ListNode* head, int m, int n) {
        if (m ==1) return reverseN(head, n);

        head->next = reverseBetween(head->next, m-1, n-1);
        return head;
    }

};