Leetcode92. Reverse Linked List II反转链表

反转从位置 m 到 n 的链表。请使用一趟扫描完成反转。

说明:

1 ≤ m ≤ n ≤ 链表长度。

示例:

输入: 1->2->3->4->5->NULL, m = 2, n = 4 输出: 1->4->3->2->5->NULL

把从m到n的反转，

然后再接上去。

 class Solution 
 {
 public:
	 ListNode * reverseBetween(ListNode* head, int m, int n) 
	 {
		 int cnt = 0;
		 ListNode* ansHead = NULL;
		 ListNode* reverseHead = NULL;
		 ListNode* lastNode = NULL;
		 ListNode* tail = NULL;
		 while (head != NULL)
		 {
			 ListNode *node = new ListNode(head->val);
			 cnt++;
			 if (cnt == m && m != n)
			 {
				 tail = lastNode;
				 if (reverseHead == NULL)
				 {
					 reverseHead = node;
					 lastNode = reverseHead;
					 head = head->next;
				 }
				 while (head != NULL)
				 {
					 ListNode *node = new ListNode(head->val);
					 cnt++;
					 node->next = lastNode;
					 lastNode = node;
					 head = head->next;
					 if (cnt == n)
					 {
						 break;
					 }
				 }
				 if (tail == NULL)
				 {
					 ansHead = lastNode;
					 lastNode = reverseHead;
				 }
				 else
				 {
					 tail->next = lastNode;
					 lastNode = reverseHead;
				 }
			 }
			 else
			 {
				 if (ansHead == NULL)
				 {
					 ansHead = node;
					 lastNode = ansHead;
				 }
				 else
				 {
					 lastNode->next = node;
					 lastNode = node;
				 }
				 head = head->next;
			 }
		 }
		 return ansHead;
	 }
 };