###### tags: `Leetcode` `easy` `list` `bit` `python` `c++`

# 1290. Convert Binary Number in a Linked List to Integer

## [題目連結:] https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/description/

## 題目:
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.


## 解題想法:
* 題目為求List中，二進位轉十進位
* head.val為最高位元

* 初始最終res=head.val
* while遍歷list
* 每次將res**左移**，並與head.next.val進行**或**運算
* head=head.next

## Python:

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def getDecimalValue(self, head):
        """
        :type head: ListNode
        :rtype: int
        """
        res=head.val
        while head.next:
            res=(res<<1)|head.next.val
            head=head.next
        return res

## C++:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    int getDecimalValue(ListNode* head) {
        int res=head->val;
        while (head->next){
            res=(res<<1)|head->next->val;
            head=head->next;
        }
        return res;
    }
};