Reverse a linked list from position m to n. Do it in-place and in one-pass.
For example:
Given 1->2->3->4->5->NULL
, m = 2 and n = 4,
return 1->4->3->2->5->NULL
.
Note:
Given m, n satisfy the following condition:
1 ≤ m ≤ n ≤ length of list.
ListNode *reverseBetween(ListNode *head, int m, int n) { ListNode *newHead = new ListNode(-1); newHead->next = head; ListNode *p = head, *pre = newHead; int cnt = 0; while(cnt < m-1) {pre = p;p=p->next;cnt++;} ListNode *q = p; p=p->next;cnt++; while(cnt< n){ ListNode *node = p->next; p->next=pre->next; pre->next = p; p = node; q->next = node; cnt++; } return newHead->next; }