leetcodes

reverse_linked_list.py

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

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        if head is None or head.next is None:
            return head
        stack = to_stack(head)
        head = ListNode(stack.pop())
        cur = head
        while stack:
            cur.next = ListNode(stack.pop())
            cur = cur.next
        return head

def to_stack(head: ListNode):
    stack = []
    cur = head
    while cur:
        stack.append(cur.val)
        cur = cur.next
    return stack



import unittest
class TestSolution(unittest.TestCase):

    def test_reverse(self):
        linked = ListNode(1)
        linked.next = ListNode(2)
        linked.next.next = ListNode(3)
        linked.next.next.next = ListNode(4)
        linked.next.next.next.next = ListNode(5)

        result = Solution().reverseList(linked)
        self.assertEqual(result.val, 5)
        self.assertEqual(result.next.val, 4)