題目

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

進階:
你可以迭代或遞迴地反轉連結串列。你能否用兩種方法解決這道題？

python程式碼實現L:

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

class Solution:
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head or not head.next:
            return head
        last = None 
        while head:
            
            t = head.next
            head.next = last
            last = head
            head = t
        return last
 

方法二：

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

class Solution:
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """

        if head is None:
            return
        if head.next is None:
            p = head
        else:
            t=Solution()
            p = t.reverseList(head.next)
            head.next.next = head
            head.next = None
        return p