leetcode-反转链表206

Posted 2020-12-10 hornets

206. 反转链表

反转一个单链表。

示例:

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

进阶:
你可以迭代或递归地反转链表。你能否用两种方法解决这道题？

class Node():    
    def __init__(self, data):
        self.val = data
        self.next = None

def reverse(head):
   	"""记录三个节点，前一个prev节点，当前cure节点，和next下个节点"""
    root = head
    res = None
    while root is not None:
        next_node = root.next # 记录下一个
        root.next = res       # 当前指向前一个
        res = root            # 当前赋值给前一个，也就是整体后移
        root = next_node	  # next赋值给当前，也就是整体后移
    return res

if __name__ == "__main__":
    node1 = Node(1)
    node2 = Node(2)
    node3 = Node(3)
    node4 = Node(4)
    node5 = Node(5)
    
    node1.next = node2
    node2.next = node3
    node3.next = node4
    node4.next = node5
    
    print(reverse(node1).val)