力扣labuladong——一刷day15

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前言

一、力扣92. 反转链表 II

/*** 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 {ListNode post;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){post = head.next;return head;}ListNode last = reverseN(head.next,n-1);head.next.next = head;head.next = post;return last;}
}

二、力扣206. 反转链表

/*** 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 reverseList(ListNode head) {if(head == null || head.next == null){return head;}ListNode last = reverseList(head.next);head.next.next = head;head.next = null;return last;}
}