Problem description

Problem on leetcode

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.


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

Input: head = [0] Output: 0

Input: head = [1] Output: 1

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

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


My guess is the problem just wants to see if we can iterate through the singly-linked list to its end, with a check for null to signify the end. While we do so, we can keep track of each node's value and return a binary value at the end.

Here's how I can express that in JavaScript:

 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 * = null;
 * }
 * @param {ListNode} head
 * @return {number}
var getDecimalValue = function(head) {
    let value = head.val.toString();
    while ( {
        head =
        value += head.val.toString();
    return parseInt(value, 2);

We start value with the string of the given head value, then while there is a next node, we set head to the current and concatenate its val to our final value return, which we return with parseInt() base 2.