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
代码
class Solution {
public:
ListNode *reverseBetween(ListNode *head, int m, int n) {
ListNode *dummy = new ListNode(-1);
dummy->next = head;
ListNode *cur = dummy;
ListNode *pre, *front, *last;
for (int i = 1; i <= m - 1; ++i) cur = cur->next;
pre = cur;
last = cur->next;
for (int i = m; i <= n; ++i) {
cur = pre->next;
pre->next = cur->next;
cur->next = front;
front = cur;
}
cur = pre->next;
pre->next = front;
last->next = cur;
return dummy->next;
}
};
