题解 | #反转链表#

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
import java.util.*;

public class Solution {
    public ListNode ReverseList(ListNode head) {
        if(head==null)
            return head;
        Stack<ListNode> stack = new Stack<ListNode>();
        stack.push(head);
        ListNode node = head;
        while(node.next!=null){
            
            stack.push(node.next);
            node=node.next;

        }
        ListNode newhead = stack.pop();
        ListNode currentNode = newhead;
        while(stack.size()>0){
            currentNode.next=stack.pop();

            currentNode=currentNode.next;
        }
        currentNode.next=null;
        return newhead;
    }
}