Convert binary number in a linked list to integer

We will use a variable res to store the result. We will iterate over the linked list, and for each node, we will shift res to the left by 1 bit, and add the value of the current node to res. Finally, we will return res.

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next

class Solution:
    def getDecimalValue(self, head: ListNode) -> int:
        res = 0
        while head:
            res = 2*res + head.val
            head = head.next
        return res

Time Complexity: O(n)
Space Complexity: O(1)