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 ) {
    // write code here
    struct ListNode* pnext = NULL;
    struct ListNode* ppre = NULL;
    struct ListNode* p = NULL;
    struct ListNode* plast = NULL;
    struct ListNode* pfirst = NULL;
    int i=0;

    if(head == NULL||head->next==NULL)
        return head;
    else
    {
        p = head;

        if(m==1)
        {
            if(n==1)
            {
                return p;
            }

            ppre = head;
            plast = head;//记一下

            for(i=0;i<n-m+1;i++)
            {
                if(i==0)
                    pfirst=head;
                pnext = head->next;
                head->next =ppre;
                ppre = head;
                head = pnext;
                p = ppre;
            }

            pfirst->next = head;

            return p;
        }
        else
        {
            for(i=0;i<m-1;i++)
            {
                ppre = head;
                plast = head;//记一下
                head = head->next;
            }

            for(i=0;i<n-m+1;i++)
            {
                if(i==0)
                    pfirst=head;
                pnext = head->next;
                head->next =ppre;
                ppre = head;
                head = pnext;
            }

            plast->next = ppre;
            pfirst->next = head;

            return p;
        }
    }
}