Convert Binary Number in a Linked List to Integer

Convert Binary Number in a Linked List to Integer

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 1:

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

Example 2:

Input: head = [0]
Output: 0

Example 3:

Input: head = [1]
Output: 1

Example 4:

Input: head = [1,0,0,1,0,0,1,1,1,0,0,0,0,0,0]
Output: 18880

Example 5:

Input: head = [0,0]
Output: 0

Constraints:

• The Linked List is not empty.

• Number of nodes will not exceed 30.

• Each node's value is either 0 or 1.

Solutions

🧠 Cpp

/**
 * 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)
    {
        string binary_s;
        for(; head; head = head->next)
            binary_s += to_string(head->val);

        return std::stoi(binary_s, nullptr, 2);
        /*
        bitset<32> binary_b;
        for(size_t i = 0, len = binary_s.size();
            i < len;
            ++i)
            binary_b[i] = binary_s[len-1-i] == '1';

        return static_cast<int>(binary_b.to_ulong());
        */
    }
};