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"""

Write a function to delete a node (except the tail)

in a singly linked list, given only access to that node.

Supposed the linked list is 1 -> 2 -> 3 -> 4 and

you are given the third node with value 3,

the linked list should become 1 -> 2 -> 4 after calling your function.

"""

import unittest

class Node:

def __init__(self, x):

self.val = x

self.next = None

def delete_node(node):

if node is None or node.next is None:

raise ValueError

node.val = node.next.val

node.next = node.next.next

class TestSuite(unittest.TestCase):

def test_delete_node(self):

# make linkedlist 1 -> 2 -> 3 -> 4

head = Node(1)

curr = head

for i in range(2, 6):

curr.next = Node(i)

curr = curr.next

# node3 = 3

node3 = head.next.next

# after delete_node => 1 -> 2 -> 4

delete_node(node3)

curr = head

self.assertEqual(1, curr.val)

curr = curr.next

self.assertEqual(2, curr.val)

curr = curr.next

self.assertEqual(4, curr.val)

curr = curr.next

self.assertEqual(5, curr.val)

tail = curr

self.assertIsNone(tail.next)

self.assertRaises(ValueError, delete_node, tail)

self.assertRaises(ValueError, delete_node, tail.next)

if __name__ == '__main__':

unittest.main()