【LeetCode】Reverse Linked List II

简单。就不解释了...（貌似内容无中文容易被CU判定为advertise给删掉...所以说这么句废话...）

/**
 * Definition for singly-linked list.
 * struct ListNode {
 * int val;
 * ListNode *next;
 * ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *reverseBetween(ListNode *head, int m, int n) {
        if(m==n) return head;
        int cnt=m;
        ListNode *pre=NULL;
        ListNode *h=head;
        while(h&&--cnt) {pre=h;h=h->next;}
        ListNode *n1=h;
        ListNode *n2=h->next;
        ListNode *n3=NULL;
        n=n-m;
        while(n1&&n2&&n--)
        {
            n3=n2->next;
            n2->next=n1;
            n1=n2;
            n2=n3;
        }
        h->next=n3;
        if(pre) pre->next=n1;
        else head=n1;
        return head;
    }
};