Convert Binary Number in a Linked List to Integer
Easy · Linked Lists · Linked List · Math · Bit Manipulation
Problem
Each node of a singly linked list holds one bit, 0 or 1. Read from head to tail, the list is a binary number with the most significant bit first.
Return the decimal value of that number.
Examples
Input: head = [1,1,0,1] Output: 13
1101 in binary is 8 + 4 + 1 = 13.
Input: head = [0] Output: 0
A single 0 bit is zero.
Input: head = [0,0,1,0] Output: 2
Leading zeros add nothing: 0010 is 2.
Constraints
- The list has between 1 and 30 nodes
- Every Node.val is 0 or 1
Approaches
- Baseline: copy the bits, then add place values — time O(n), space O(n)
Follow-up
The list holds at most 30 bits, so the value fits a 32-bit signed integer. For longer numbers you would return the value modulo a prime, applying the modulus after every step; the use cases do that for other bases, and read the bits least significant first.
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