class Solution {
public:
ListNode* reverseBetween(ListNode* head, int m, int n) {
ListNode* new_head = new ListNode(0);
new_head -> next = head;
ListNode* pre = new_head;
for (int i = 0; i < m - 1; i++)
pre = pre -> next;
ListNode* cur = pre -> next;
for (int i = 0; i < n - m; i++) {
ListNode* move = cur -> next;
cur -> next = move -> next;
move -> next = pre -> next;
pre -> next = move;
}
return new_head -> next;
}
};