---
title: 'LeetCode 1290. Convert Binary Number in a Linked List to Integer'
disqus: hackmd
---

# LeetCode 1290. 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.

## Example

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

## Constraints

The Linked List is not empty.
Number of nodes will not exceed 30.
Each node's value is either 0 or 1.

## Answer

此題可將list中的val一個個抓出來疊加，並將舊值<<1上去，即可得答案。

//2021_11_29
int getDecimalValue(struct ListNode* head) {
    int ans = 0;
    while(head){
        ans = (ans << 1) | head->val;
        head = head->next;
    }
    return ans;
}

## Link
https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/
###### tags: `Leetcode`