---
title : Convert Binary Number in a Linked List to Integer
tags :
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###### tags: `LeetCode`,

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

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

Problem Analytica
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This problem is to convert a linkedlist binary number i.e. $(101)_2$ into an integer $1\cdot 2^2 + 0 \cdot 2^1 + 1 \cdot 2^0 = 5$

Point of Attack
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:::spoiler Spoiler Alert
Since the list is starting from higher order digit `1->0->1` , we can simply apply arithmetic $(((1)\cdot2+0)\cdot2)+1) \equiv 1\cdot 2^2 + 0 \cdot 2^1 + 1 \cdot 2^0$

Borrowing the very explainning graph from leet code solution

The solution is quite straight forward
:::

Algorithm
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:::spoiler Spoiler Alert

    int getDecimalValue(ListNode* head){
        int value = 0;
        while(head != nullptr){
            value = (value << 1) | head->val;
            head = head->next;
        }
        return value;        
    }

:::

Hierarcy Decompsition
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Further Readings
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###### tags: `LeetCode`, `Bit Manipulation`