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
        ListNode* empty_node = new ListNode(-1);
        empty_node->next = head;
        //取翻转起始节点前一个
        ListNode* pre = empty_node;
        for(int i = 0;i < m - 1;i++)
        {
            pre = pre->next;
        }
        ListNode *beginNode = pre->next;
        // 取翻转终止节点后一个
        ListNode *endNode = pre;
        for(int i = 0;i < n - m + 1; i++)
        {
            endNode = endNode->next;
        }
        ListNode* succ = endNode->next;

        endNode->next = nullptr;
        reverseList(beginNode);
        pre->next = endNode;
        beginNode->next = succ;
        return empty_node->next;
    }

    ListNode* reverseList(ListNode* head)
    {
        ListNode* cur = head;
        ListNode* pre = nullptr;
        while (cur) {
            ListNode* next = cur->next;
            cur->next = pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }
};