```
import random
class ListNode(object):
def __init__(self, x):
self.val = x
self.next = None
head= ListNode(2)
head.next = ListNode(3)
head.next.next = ListNode(4)
class Solution(object):
def __init__(self, head):
self.head = head
length = 1
tmp = self.head.next
while tmp is not None:
length += 1
tmp = tmp.next
self.length = length
def getRandom(self):
index = random.randrange(0, self.length)
tmp = self.head
while index > 0:
tmp = tmp.next
index -= 1
return tmp
a = Solution(head=head)
print(a.getRandom().val)
```

The input is:

```
["Solution","getRandom"]
[[[1,2,3]],[]]
```

Your answer:

```
[null,[3]]
```

Expected answer:

```
[null,3]
```