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

Problem #

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.

Problem Summary #

You are given the reference node head of a singly linked list. The value of each node in the linked list is either 0 or 1. This linked list is known to be the binary representation of an integer. Return the decimal value represented by this linked list.

Notes:

• The linked list is not empty.
• The total number of nodes in the linked list does not exceed 30.
• Each node’s value is either 0 or 1.

Solution Approach #

• Given a linked list, the number represented from head to tail is the binary form of an integer; output the decimal value of this integer.
• This is an easy problem. Traverse the linked list once from head to tail, accumulating the binary bits as you go.

Code #

func getDecimalValue(head *ListNode) int {
	sum := 0
	for head != nil {
		sum = sum*2 + head.Val
		head = head.Next
	}
	return sum
}