###### tags: `LeetCode Study Group - LinkedList` `LeetCode Easy` `LeetCode Study Group`
# 1290. Convert Binary Number in a Linked List to Integer
Link: https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/description/

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.

The most significant bit is at the head of the linked list.

Example 1:

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

Example 2:

Input: head = [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.

## Solution-1

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

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public int getDecimalValue(ListNode head) {
        ListNode node = head;
        int res = 0;
        while(node != null){
            res = res * 2 + node.val;
            node = node.next;
        }
        return res;
    }
}

## Reference
https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/solutions/851040/convert-binary-number-in-a-linked-list-to-integer/