466. Count Linked List Nodes

[ http://www.lintcode.com/en/problem/count-linked-list-nodes/ ]

# Python
"""
Definition of ListNode
class ListNode(object):

    def __init__(self, val, next=None):
        self.val = val
        self.next = next
"""


class Solution:
    """
    @param: head: the first node of linked list.
    @return: An integer
    """
    def countNodes(self, head):
        # write your code here
        p = head
        count = 0
        while p != None:
            p = p.next
            count += 1
        return count