Given the head of a singly linked list and two integers left and right where left <= right, reverse the nodes of the list from position left to position right, and return the reversed list.
Example 1:
Input: head = [1,2,3,4,5], left = 2, right = 4
Output: [1,4,3,2,5]
Example 2:
Input: head = [5], left = 1, right = 1
Output: [5]
Constraints:
- The number of nodes in the list is n.
- 1 <= n <= 500
- -500 <= Node.val <= 500
- 1 <= left <= right <= n
Follow up: Could you do it in one pass?
非递归
class Solution {
public ListNode reverseBetween(ListNode head, int left, int right) {
ListNode temp = new ListNode(0);
temp.next = head;
// 先移动left步
ListNode cur1 = temp;
ListNode pre1 = null;
for(int i=0;i<left;i++){
pre1 = cur1;
cur1 = cur1.next;
}
//reverse
ListNode cur2 = cur1;
ListNode pre2 = pre1;
for(int i=left;i<=right;i++){
ListNode next = cur2.next;
cur2.next = pre2;
pre2 = cur2;
cur2 = next;
}
//connect
pre1.next = pre2;
cur1.next = cur2;
return temp.next;
}
}递归
class Solution {
private ListNode successor = null;
public ListNode reverseBetween(ListNode head, int left, int right) {
if(left == 1){
return reverseN(head, right);
}
head.next = reverseBetween(head.next, left - 1, right - 1);
return head;
}
public ListNode reverseN(ListNode head, int n){
if(n==1){
successor = head.next;
return head;
}
ListNode last = reverseN(head.next, n-1);
head.next.next = head;
head.next = successor;
return last;
}
}