算法-02-反转链表

 描述

输入一个链表，反转链表后，输出新链表的表头。

Java 

/*
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)
           return null;
        else
           return reverserList(head);
    }
    
    public ListNode reverserList(ListNode head){
        if(head.next==null)
           return head;
        ListNode last = ReverseList(head.next);
        head.next.next = head;
        head.next = null;
        return last;
    }
}

Python

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    # 返回ListNode
    def ReverseList(self, pHead):
        # write code here
        if pHead is None:
            return None
        else:
            return self.reverseList(pHead)
        
    def reverseList(self, pHead):
        if pHead.next is None:
            return pHead
        else:
            last = self.reverseList(pHead.next)
            pHead.next.next = pHead
            pHead.next = None
            return last