Convert Binary Number in a Linked List to Integer
<p>Given <code>head</code> which is a reference node to a singly-linked list. The value of each node in the linked list is either <code>0</code> or <code>1</code>. The linked list holds the binary representation of a number.</p>

<p>Return the <em>decimal value</em> of the number in the linked list.</p>

<p>The <strong>most significant bit</strong> is at the head of the linked list.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1200-1299/1290.Convert%20Binary%20Number%20in%20a%20Linked%20List%20to%20Integer/images/graph-1.png" style="width: 426px; height: 108px;" />
<pre>
<strong>Input:</strong> head = [1,0,1]
<strong>Output:</strong> 5
<strong>Explanation:</strong> (101) in base 2 = (5) in base 10
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> head = [0]
<strong>Output:</strong> 0
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The Linked List is not empty.</li>
	<li>Number of nodes will not exceed <code>30</code>.</li>
	<li>Each node&#39;s value is either <code>0</code> or <code>1</code>.</li>
</ul>
Linked List; Math
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public int GetDecimalValue(ListNode head) {
        int ans = 0;
        for (; head != null; head = head.next) {
            ans = ans << 1 | head.val;
        }
        return ans;
    }
}