C++ Program To Find Decimal Equivalent Of Binary Linked List

Given a singly linked list of 0s and 1s find its decimal equivalent.

Input: 0->0->0->1->1->0->0->1->0
Output: 50   

Input: 1->0->0
Output: 4

The decimal value of an empty linked list is considered as 0.

Initialize the result as 0. Traverse the linked list and for each node, multiply the result by 2 and add the node’s data to it.

C++

// C++ Program to find decimal value
// of binary linked list
#include <bits/stdc++.h>
using namespace std;

// Link list Node
class Node
{
    public:
    bool data;
    Node* next;
};

/* Returns decimal value of binary
   linked list */
int decimalValue(Node *head)
{
    // Initialized result
    int res = 0;

    // Traverse linked list
    while (head != NULL)
    {
        // Multiply result by 2 and
        // add head's data
        res = (res << 1) + head->data;

        // Move next
        head = head->next;
    }
    return res;
}

// Utility function to create a
// new node.
Node *newNode(bool data)
{
    Node *temp = new Node;
    temp->data = data;
    temp->next = NULL;
    return temp;
}

// Driver code
int main()
{
    // Start with the empty list
    Node* head = newNode(1);
    head->next = newNode(0);
    head->next->next = newNode(1);
    head->next->next->next = newNode(1);
    cout << "Decimal value is " <<
             decimalValue(head);
    return 0;
}
// This is code is contributed by rathbhupendra

Output :

Decimal value is 11

Time Complexity: O(n) where n is the number of nodes in the given linked list.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Another Approach(by reversing the Linked List):
Follow the below steps to solve the given problem
1) First reverse the given linked list.
2) Initialize a ans variable to store ans and pos variable to keep track of position of node in linked list.
3) Perform the operation ans = ans + (rhead.data*(2**pos))%MOD)
4) perform ans = ans%MOD

Below is the implementation of above approach:

C++

#include<bits/stdc++.h>
using namespace std;
// C++ Program to find decimal value
// of binary linked list

// node structure
struct Node{
    int data;
    Node* next;
    Node(int data){
        this->data = data;
        this->next = NULL;
    }
};

long long unsigned int power(int num,int count){
if(count ==0) return 1;
if(count%2==0)
    return (power(num,count/2)%1000000007)*(power(num,count/2)%1000000007);
else
    return num*(power(num,count/2)%1000000007)*(power(num,count/2)%1000000007);;
}

Node* reverse(Node* head){
    if(head == NULL || head->next == NULL) return head;

    Node* curr = head;
    Node* prev = NULL;
    Node* nxt = head->next;
    while(nxt != NULL){
        curr->next = prev;
        prev = curr;
        curr = nxt;
        nxt = nxt->next;
    }
    curr->next = prev;
    return curr;
}

int decimalValue(Node* head){
    int MOD = 1000000007;
    Node* rhead = reverse(head);

    int ans = 0;
    int pos = 0;
    while(rhead != NULL){
        ans = (ans%MOD + ((rhead->data)*power(2,pos)) % MOD) % MOD;
        rhead = rhead->next;
        pos++;
    }
    return ans;
}

int main(){
    Node* head = new Node(1);
    head->next = new Node(0);
    head->next->next = new Node(1);
    head->next->next->next = new Node(1);

    cout<<"Decimal Value is : "<<decimalValue(head);
}

Output

Decimal Value is : 11

Time Complexity: O(N) where N is the number of nodes in linked list.
Auxiliary Space: O(1)

Please refer complete article on Decimal Equivalent of Binary Linked List for more details!