力扣92.反转链表Ⅱ

 

将自己的思路记录一下

题目：【https://leetcode.cn/problems/reverse-linked-list-ii/description/?envType=study-plan-v2&envId=top-interview-150】

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* reverseBetween(struct ListNode* head, int left, int right) {
    if (left >= right)
        return head;
    struct ListNode* prev = NULL;
    struct ListNode* curr = head;
    struct ListNode* next = NULL;

    for (int i = 1; i < left; ++i) {
        prev = curr;
        curr = curr->next;
    }
    struct ListNode* start = curr;

    for (int i = 0; i <= right - left; ++i) {
        next = curr->next;
        curr->next = prev;
        prev = curr;
        curr = next;
    }

    if (start->next) start->next->next = prev;
    start->next = curr;
    return left <= 1 ? prev : head;
}