## Description

https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/

Given `head`

which is a reference node to a singly-linked list. The value of each node in the linked list is either 0 or 1. The linked list holds the binary representation of a number.

Return the *decimal value* of the number in the linked list.

**Example 1:**

Input:head = [1,0,1]Output:5Explanation:(101) in base 2 = (5) in base 10

**Example 2:**

Input:head = [0]Output:0

**Example 3:**

Input:head = [1]Output:1

**Example 4:**

Input:head = [1,0,0,1,0,0,1,1,1,0,0,0,0,0,0]Output:18880

**Example 5:**

Input:head = [0,0]Output:0

**Constraints:**

- The Linked List is not empty.
- Number of nodes will not exceed
`30`

. - Each node’s value is either
`0`

or`1`

.

## Explanation

Multiply result by 2.

## Python Solution

```
# 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:
result = 0
while head:
result = result * 2 + head.val
head = head.next
return result
```

- Time Complexity: O(N)
- Space Complexity: O(1)