link.py

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

class Solution(object):

    def __init__(self, head):
        """
        @param head The linked list's head.
        Note that the head is guaranteed to be not null, so it contains at least one node.
        :type head: ListNode
        """
        self.ll = head
        self.length = 0
        while head:
            self.length += 1
            head = head.next
        

    def getRandom(self):
        """
        Returns a random node's value.
        :rtype: int
        """
        import random
        r = random.randint(1,self.length)
        count = 1
        h = self.ll
        while h and count <= r:
            if count == r:
                return h.val
            count += 1
            h = h.next
        


# Your Solution object will be instantiated and called as such:
# obj = Solution(head)
# param_1 = obj.getRandom()