反转从位置 m 到 n 的链表。请使用一趟扫描完成反转。

Posted 2022-03-21 q-1993

/**
 * Definition for singly-linked list.
 * public class ListNode 
 *     int val;
 *     ListNode next;
 *     ListNode(int x)  val = x; 
 * 
 */
class Solution 
    public ListNode reverseBetween(ListNode head, int m, int n) 
       if (head == null || head.next == null) 
            return head;
        
        ListNode newHead = new ListNode(0);
        newHead.next = head;
        ListNode pre = newHead;
        int count = 1;
        while (pre !=  null && count != m) 
            pre = pre.next;
            count++;
        
        ListNode leftNode = pre.next;
        pre.next = null;
        ListNode temp=null;
        count--;
        while(leftNode!=null && count < n) 
            count++;
            temp = leftNode;
            leftNode = leftNode.next;
            temp.next = pre.next;
            pre.next = temp;
        
       while(pre.next!=null) 
          pre = pre.next; 
       
        pre.next = leftNode;
        return newHead.next;