各种错法:

  1. prev 初始化为ListNode(0)而不是null;
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public ListNode reverseList(ListNode head) {
        ListNode prev = new ListNode(0); 
        
        while (head != null) {
            ListNode next = head.next;
            head.next = prev;
            prev = head;
            head = next;
        }
        return prev;
    }

Submission : Wrong Answer

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Input: [1,2,3,4,5]
Output: [5,4,3,2,1,0]
Expected: [5,4,3,2,1]

  1. prev 初始化带有自己的next:
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    public ListNode reverseList(ListNode head) {
        ListNode prev = new ListNode(0); 
        prev.next = head;

        while (head != null) {
            ListNode next = head.next;
            head.next = prev;
            prev = head;
            head = next;
        }
        return prev;
    }

Submission : N/A

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Input: [1,2,3,4,5]
Output: Found cycle in the ListNode
Expected: [5,4,3,2,1]

Correct:

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public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        
        while (head != null) {
            ListNode next = head.next;
            head.next = prev;
            prev = head;
            head = next;
        }
        return prev;
    }