leetcode-面试题24-反转链表

方法一：迭代

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode pre = null;
        ListNode cur = head;
        ListNode tmp = null;
        while(cur!=null){
            tmp = cur.next;
            cur.next = pre;
            pre = cur;
            cur = tmp;
        }
        return pre;
    }
}

方法二：递归

class Solution {
    public ListNode reverseList(ListNode head) {
        if(head==null || head.next==null){
            return head;
        }
        ListNode cur = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return cur;
    }
}

 方法三：妖魔化迭代

class Solution {
    public ListNode reverseList(ListNode head) {
        if(head==null ){
            return null;
        }
        ListNode cur = head;
        while(head.next!=null){
            ListNode tmp = head.next.next;
            head.next.next = cur;
            cur = head.next;
            head.next = tmp;
        }
        return cur;
    }
}