【Leetcode】19. Remove Nth Node From End of List

 1 /**
 2 * Definition for singly-linked list.
 3 * struct ListNode {
 4 *     int val;
 5 *     ListNode *next;
 6 *     ListNode(int x) : val(x), next(NULL) {}
 7 * };
 8 */
 9 class Solution
10 {
11 public:
12     ListNode * removeNthFromEnd(ListNode* head, int n)
13     {
14         ListNode *h = head, *h1;
15 
16         if (head != nullptr)
17         {
18             int num = 1;
19             while (h->next != nullptr)
20             {
21                 ++num;
22                 h = h->next;
23             }
24             if (n == 0 || n > num)
25                 return head;
26             else if (n == num)
27             {
28                 h = head;
29                 head = head->next;
30                 free(h);
31                 return head;
32             }
33             else
34             {
35                 h = head;
36                 while (h->next != NULL)
37                 {
38                     if (num == n + 1)
39                         h1 = h;
40                     --num;
41                     h = h->next;
42                 }
43                 h = h1->next;
44                 h1->next = h->next;
45                 free(h);
46                 return head;
47             }
48         }
49         else
50             return head;
51     }
52 };