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

Description

https://leetcode.com/problems/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.

Explanation

Multiply result by 2.

Python Solution

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def getDecimalValue(self, head: ListNode) -> int:
        result = 0
        
        while head:
            result = result * 2 + head.val
            head = head.next
                
        return result
  • Time Complexity: O(N)
  • Space Complexity: O(1)

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