Leetcode206. 反轉鏈表

反轉一個單鏈表。

示例:

輸入: 1->2->3->4->5->NULL
輸出: 5->4->3->2->1->NULL

思路

一個空節點起着至關重要的作用。

# Definition for singly-linked list.
class ListNode(object):
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        cur = head
        pre = None
        while cur!= None:
            n = cur.next
            cur.next = pre
            pre = cur
            cur = n
        
        return pre