题目描述
输入一个链表，反转链表后，输出新链表的表头。
法一：迭代法
/*
public class ListNode {
int val;
ListNode next = null; ListNode(int val) {
this.val = val;
}
}*/
public class Solution {
public ListNode ReverseList(ListNode head) {
if(head == null)
return null;
ListNode pre = null;
ListNode next = null; while(head != null){
next = head.next;
head.next = pre;
pre = head;
head = next;
}
return pre;
}
}
法二：递归法
/*
public class ListNode {
int val;
ListNode next = null; ListNode(int val) {
this.val = val;
}
}*/
public class Solution {
public ListNode ReverseList(ListNode head) {
if(head == null ||head.next == null)
return head;
ListNode next = head.next;
head.next = null;
ListNode newHead = ReverseList(next);
next.next = head;
return newHead;
}
}