[Leetcode reverse list II]

Topic links: reverse list II

The meaning of problems: reversed from the position  m  to  n  list. Please use the trip to the scan is complete reversal.

Description:
. 1 ≤  m  ≤  n-  ≤ chain length.

Input: l-> 2-> 3-> 4-> 5-> NULL, m = 2, n- =. 4

Output: 1-> 4-> 3-> 2-> 5-> NULL

Solution: feeling is the k-th set of inverted list changed next. . Also the simpler. Go of m, then reversed from m to n. You can view links.

 

Code:

 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 public:
11     ListNode* reverseBetween(ListNode* head, int m, int n) {
12         
13         ListNode* ans = new ListNode(0);
14         ListNode* pre = ans;
15         ListNode* cur = head;
16         ListNode* tail = ans;
17         ans->next = head;
18 
19         for(int i = 1; i < m;i++){
20             head = head->next;
21             pre = cur;
22             cur = head;
23         }
24 
25         for(int i = m;i < n;i++){
26             tail = cur->next;
27 
28             cur->next = tail->next;
29             tail->next = pre->next;
30             pre->next = tail;
31         }
32 
33         return ans->next;
34 
35     }
36 };