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 || head.next == null) {
            return head;
        }

        ListNode result = head;
        ListNode tempHead = head.next;
        result.next = null;

        while(tempHead != null) {
            ListNode tempNext = tempHead.next;

            tempHead.next = result;

            result = tempHead;

            tempHead = tempNext;
        }

        return result;
    }
}

对于java的链表而言，在将head赋值给result之后，不能直接进行result.next=null，这样会导致head的后续值全丢失，这是因为java的赋值是进行引用赋值，操作的还是同一个地址保存的数值，所以在进行result.next=null之前需要将head.next的值进行保存