单链表反转

1.

# Definition for singly-linked list.
class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next


class Solution:
    def reverseList(self, head: ListNode):
        pre = None
        curr = head
        while curr:
            # 先把下一个节点保存下来放到next变量中
            next = curr.next
            # 先把当前节点的下一个节点指向pre
            curr.next = pre
            # 再把当前结点赋值给pre
            pre = curr
            # 继续下一个节点的反转
            curr = next
        return pre

if __name__ == '__main__':
    node = ListNode(1)
    node.next = ListNode(2)
    node.next.next = ListNode(3)
    node.next.next.next = ListNode(4)
    node.next.next.next.next = ListNode(5)
    s = Solution().reverseList(node)