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 ) {
    if(head == NULL) return NULL;
    if(m == 0 || n <= m) return head;
    struct ListNode* begin = head;
    int i = 1;
    while(i < m)
    {
        begin = begin->next;
        i++;    
    }//顺序遍历链表到节点m

    struct ListNode* pre = begin;
    struct ListNode* cur = begin->next;
    while(i < n)
    {
        struct ListNode* temp = cur->next;
        cur->next = pre;
        pre = cur;
        cur = temp;
        i++;
    }//反转链表
    begin->next = cur;//连接节点n之后的节点
    
    int j = 1;
    struct ListNode* start = head;
    while(j<m-1)
    {
        start = start->next;
        j++;   
    }//顺序遍历链表到节点m-1
    
    if(m>1)
    {
        start->next = pre;
        return head;//如果m节点不是头节点，则需要将m-1节点连接到pre节点
    }
    else
    {
        return pre;
    }

}