题解 | 反转链表

/*
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;
        int cnt=0;
        int[] arr= new int[101000];
        for(;head!=null;head=head.next){
            arr[cnt++]=head.val;
        }
        ListNode ans,p;
        ans=new ListNode(arr[cnt-1]);
        p=ans;
        for(int i=cnt-2;i>=0;i--){
            p.next=new ListNode(arr[i]);
            p=p.next;
        }
        return ans;
    }
}