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* reverseBetween(ListNode* head, int m, int n) {
        // write code here
        if (m == n) {
            return head;
        }

        auto raw_head = head;
        auto pre = head;
        for (auto i = 1; i < m; ++i) {
            pre = head;
            head = head->next;
        }

        ListNode* sub_head = nullptr;
        ListNode* next = head->next;
        ListNode* sub_tail = head;
        for (auto i = m; i <= n; ++i) {
            head->next = sub_head;
            sub_head = head;
            head = next;
            if (head != nullptr) {
                next = head->next;
            }
        }

        if (m != 1) {
            pre->next = sub_head;
        } else {
            raw_head = sub_head;
        }
        
        sub_tail->next = head;

        return raw_head;
    }
};