Formatted question description: https://leetcode.ca/all/1290.html

1290. Convert Binary Number in a Linked List to Integer (Easy)

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.

Related Topics:
Linked List, Bit Manipulation

Solution 1.

// OJ: https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/

// Time: O(N)
// Space: O(1)
class Solution {
public:
    int getDecimalValue(ListNode* head) {
        int ans = 0;
        while (head) {
            ans = (ans << 1) + head->val;
            head = head->next;
        }
        return ans;
    }
};

Java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public int getDecimalValue(ListNode head) {
        int decimalValue = 0;
        ListNode temp = head;
        while (temp != null) {
            decimalValue <<= 1;
            decimalValue += temp.val;
            temp = temp.next;
        }
        return decimalValue;
    }
}

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