Double a Number Represented as a Linked List
A medium-tier problem at 61% community acceptance, tagged with Linked List, Math, Stack. Reported in interviews at Nvidia and 0 others.
You're given a linked list where each node holds a single digit, and the list represents a number. You need to double that number and return it as a modified linked list. Nvidia has asked this. It sounds straightforward until you realize you can't just convert to integer, double it, and convert back, especially for large numbers that overflow. The trick is handling carry propagation correctly while staying within the linked list structure. StealthCoder solves this instantly if you blank on the carry logic during your live assessment.
Companies that ask "Double a Number Represented as a Linked List"
Double a Number Represented as a Linked List is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by an Amazon engineer who used it to pass JPMorgan's OA and system design loop.
Get StealthCoderThe core pattern is carry propagation, same as grade-school multiplication. You traverse the list, double each digit, and propagate carries forward. The trap: you might process digits left-to-right and miss carries that ripple ahead, or you might try to reverse the list unnecessarily. The cleanest approach uses a stack or recursion to process from the tail, doubling each digit and handling carries cleanly. If the final carry exists, you prepend a new node. Common failures include forgetting the carry-forward step, not handling the case where doubling creates an extra digit at the front, or mismanaging pointers. StealthCoder is your safety net if the carry logic trips you up mid-interview.
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Double a Number Represented as a Linked List recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by an Amazon engineer who used it to pass JPMorgan's OA and system design loop. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Double a Number Represented as a Linked List interview FAQ
Can I just convert the linked list to an integer, double it, and convert back?+
Not reliably. The number represented by the list might be too large for standard integer types. You need to work with the linked list structure directly and handle carry propagation digit-by-digit, the way you'd do manual multiplication on paper.
Do I need to reverse the list?+
Not necessarily. A stack or recursive approach lets you process from the tail backward without reversing. Some solutions do reverse for simplicity, but it's an extra operation. Choose based on what feels natural to you during the interview.
What happens when doubling creates a carry that adds a digit?+
For example, doubling 5 gives 10, so you store 0 and carry 1. If the final carry exists after processing all nodes, prepend a new node with value 1 to the front of the list.
Is this problem still asked at top companies?+
Nvidia has asked it. It's a solid linked list and math fundamentals test. It's less common than other linked list problems but shows up often enough that you should be ready for it.
What's the main difference between this and reversing a linked list?+
Reversing is about pointers and direction. Doubling is about arithmetic and carry logic. Both test linked list fluency, but doubling adds a mathematical layer that catches people off guard if they haven't drilled it.
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