反转链表的Java实现

1. 题目

反转链表，例如，原链表1-2-3-4-5，反转后为5-4-3-2-1。

2. 迭代法实现

private ListNode reverseList(ListNode head) {
    if(head == null || head.next == null){
        return head;
    }
    ListNode cur = head.next;
    head.next = null;
    while(cur != null){
        ListNode next = cur.next;
        cur.next = head;
        head = cur;
        cur = next;
    }
    return head;
}

3. 头插法实现

private static ListNode reverseList(ListNode head) {
    if(head == null || head.next == null){
        return head;
    }
    ListNode newHead = new ListNode(0);
    while(head != null){
        ListNode next = head.next;
        head.next = newHead.next;
        newHead.next = head;
        head = next;
    }
    return newHead.next;
}