Use simple linked list traversal and binary shift to solve this problem.
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
def getDecimalValue(self, head):
ans = 0
while head:
ans = (ans << 1) + head.val
head = head.next
return ans