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力扣92.反转指定范围内的链表、25.k个一组反转链表

news 来源：原创 2025/5/10 21:59:39

92.反转指定范围内的链表

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode reverseBetween(ListNode head, int left, int right) {//left是第left个节点ListNode dummy=new ListNode(0,head);int count=0;ListNode pre=dummy,cur=dummy,tailAfter;while (right-->0){cur=cur.next;count++;if  (count==left-1){pre=cur;}}tailAfter=cur.next;cur.next=null;ListNode newHead=reverseList(pre.next);pre.next.next=tailAfter;pre.next=newHead;return dummy.next;}public ListNode reverseList(ListNode root){if (root==null || root.next==null) return root;ListNode newHead=reverseList(root.next);root.next.next=root;root.next=null;return newHead;}
}

25.k个一组反转链表

class Solution {public ListNode reverseKGroup(ListNode head, int k) {ListNode dummy=new ListNode(0,head);ListNode cur=dummy,pre=dummy,tail,tailAfter;int copyk;while (true){copyk=k;while (cur!=null && copyk-->0){cur=cur.next;}if (copyk>0 || cur==null) break;//为反转做准备tailAfter=cur.next;cur.next=null;ListNode newhead=reverseList(pre.next);pre.next.next=tailAfter;tail=pre.next;pre.next=newhead;//为下一次做准备pre=tail;cur=tail;}return dummy.next;}public ListNode reverseList(ListNode root){if (root==null || root.next==null) return root;ListNode newhead=reverseList(root.next);root.next.next=root;root.next=null;return newhead;}
}