1290. Convert Binary Number in a Linked List to Integer

Description

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.

Constraints

• The Linked List is not empty.

• Number of nodes will not exceed 30.

• Each node's value is either 0 or 1.

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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

Solutions

ListNode

// Definition for singly-linked list.
public class ListNode {
	int val;
	ListNode next;
	
	ListNode() {}
	
	ListNode(int val) {
		this.val = val;
	}
	
	ListNode(int val, ListNode next) {
		this.val = val; this.next = next;
	}
}

Solution 1

/**
 * Time complexity : O(N)
 * Space complexity : O(1)
 */

class Solution {
    public int getDecimalValue(ListNode head) {
        if(head == null) return 0;
        
        int result = 0;
        ListNode curr = head;
        
        while(curr != null) {
            result = (result*2) + curr.val;
            curr = curr.next;
        }
        
        return result;
    }
}

Solution 2

/**
 * Time complexity : O(N)
 * Space complexity : O(1)
 */
 
 class Solution {
    public int getDecimalValue(ListNode head) {
        int num = head.val;
        while (head.next != null) {
            num = (num << 1) | head.next.val;
            head = head.next;    
        }
        return num;
    }
}

Follow up