关于反向链表的问题(leetcode 206)

Question

我知道我的代码完全错了，但我不知道我做错了什么，

有人能指出并解释我做错了什么吗？

public ListNode reverseList(ListNode head) {
if (head == null) {
return head;
}

ListNode prev = null;
ListNode current = head;
ListNode nextNode = head.next;

while (nextNode != null) {
prev = current;
current = nextNode;
current.next = prev;
nextNode = nextNode.next;
System.out.println(nextNode.val);
}

return current;
}

Answer 1

更改：

1. head.next=null；//使列表的末尾为空

2. current.next=prev；//current是对节点的引用，因此对它的更改将使用引用nextNode(也称(更改节点

   public ListNode reverseList(ListNode head) {
   if (head == null) {
   return head;
   }
   ListNode prev = null;
   ListNode current = head;
   ListNode nextNode = head.next;
   head.next = null;   // to make the end of the list as null
   while (nextNode != null) {
   prev = current;
   current = nextNode;
   nextNode = nextNode.next;   // first get next node, before ...
   current.next = prev;        // ... overwriting it here
   // System.out.println(nextNode.val);
   }
   return current;
   }
   

Answer 2

替代解决方案

我们可以说while head != null，然后使用prev节点将其反转，最后我们将返回prev。这会更容易：

public final class Solution {
public static final ListNode reverseList(ListNode head) {
ListNode prev = null;
ListNode nextNode;
while (head != null) {
nextNode = head.next;
head.next = prev;
prev = head;
head = nextNode;
}
return prev;
}
}