题解 | 链表内指定区间反转

/**
 * struct ListNode {
 *  int val;
 *  struct ListNode *next;
 * };
 */
/**
 * 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
 */
struct ListNode* reverseBetween(struct ListNode* head, int m, int n ) {
    //思路
    //创建三个结点：PreviousNode，StartNode(反序的起点)，NextNode(待移动的结点)
    //将NextNode移动至PreviousNode的后面，实现反序

    struct ListNode HeadNode = { .next = head };
    struct ListNode *previousNode = &HeadNode;
    struct ListNode *startNode = NULL;
    struct ListNode *nextNode = NULL;

    if (head == NULL || m == n) {
        return head;
    }

    for (int i = 1; i < m; i++) {
        previousNode = previousNode->next;
    }

    startNode = previousNode->next;
    nextNode = startNode->next;

    for (int i = 0; i < (n - m); i++) {
        startNode->next = nextNode->next;
        nextNode->next = previousNode->next;
        previousNode->next = nextNode;
        nextNode = startNode->next;
    }
    return HeadNode.next;
}