Decimal Equivalent of Binary Linked List


The linked list is one of the most important concepts and data structures to learn while preparing for interviews. Having a good grasp of Linked Lists can be a huge plus point in a coding interview.

Problem Statement

We will be given a Binary linked list, i.e, a list where each node will be having either 0 or 1 as its data, and we need to find its decimal equivalent.

Problem Statement Understanding

Let's try to understand the problem with the help of an example:

If the linked list given to us is 1→1→0→1→NULL

  • According to the problem statement, we need to find the decimal equivalent of the given binary list.
  • We can see that the binary equivalent of the given list is 1101.
  • Now, on converting this binary equivalent 1101 into decimal, we get 13.
  • So, the output will be 13.

Let’s take another example.
If the linked list given to us is 1→1→0→1→0→1→NULL.

  • In this case, the binary equivalent of the given list is 110101.
  • Now, on converting the binary equivalent 110101 into decimal, we get 53.
  • So, the output will be 53.

At this point, we have understood the problem statement. Now we will try to formulate an approach for this problem.

Before moving to the approach section, try to think about how you can approach this problem.

  • If stuck, no problem, we will thoroughly see how we can approach this problem in the next section.

Let’s move to the approach section.


Our approach will be straightforward:

  • We will iterate the list from starting and accumulate the result in a variable.
  • While we move through the list, the position of binary numbers that have been encountered till now in our result shifts by one to the left.
    • So that’s why we will multiply our result by 21 (as there is a shift by one position) and add the current position’s data.
  • Finally, we will be left with a decimal number, which will be our final decimal representation of our binary list.


  • Initialize an ans variable by 0 and a curr pointer by the head of the list.
  • Run a while loop till the curr pointer is not NULL.
  • Every time inside the loop, multiply the ans by 2 and add the curr->data in ans.
  • Move the curr pointer by one node.
  • Return the ans after the loop breaks.

Dry Run

Code Implementation

using namespace std;

class Node {
    int data;
    Node* next;
    Node(int d)
        data = d;
        next = NULL;

// This function will return decimal
// equivalent of a binary list
int binaryToDecimal(Node *head)
    // Initialize 'ans' by 0
    int ans = 0;
    // initialize 'curr' by 'head'
    Node* curr = head;
    // run a while loop till 'curr' is not NULL
    while (curr != NULL)
        // multiply the 'ans' by 2 and add
       // 'curr' data to it
        ans = (ans * 2) + curr->data;
        // move 'curr' by one node 
        curr = curr->next;
    return ans;

int main()
    Node *list = new Node(1);
    list->next = new Node(1);
    list->next->next = new Node(0);
    list->next->next->next = new Node(1);
    cout<<"Decimal Equivalent of the given binary list is: ";



Decimal Equivalent of the given binary list is: 13

Time Complexity: O(n), where n is the number of nodes in the linked list.

So, in this blog, we have tried to explain how you can get the decimal equivalent of a binary list in the most optimal way. If you want to solve more questions on Linked List, which are curated by our expert mentors at PrepBytes, you can follow this link Linked List.

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