leetcood学习笔记-206-反转链表

题目描述：

 

解法一：迭代

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        pre = None
        cur = head
        while cur:
            tmp = cur.next
            cur.next = pre
            cur,pre = tmp,cur
        return pre

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        p,rev = head,None
        while p:
            rev,rev.next,p = p,rev,p.next
        return rev

解析：

 

 

方法二：递归

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        return self.reverse(None,head)
    
    def reverse(self,current_node,next_node):
        if next_node is None:
            return current_node
        
        temp = next_node.next
        next_node.next = current_node
        
        return self.reverse(next_node,temp)

方法三：栈

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        stack = [None]
        while head:
            stack.append(head)
            head = head.next
        p = stack.pop()
        head = p
        while head:
            head.next = stack.pop()
            head = head.next
        return p