Add Two Numbers II
A medium-tier problem at 62% community acceptance, tagged with Linked List, Math, Stack. Reported in interviews at Juniper Networks and 0 others.
Add Two Numbers II shows up in live assessments and hits different than the original. You've got two linked lists representing numbers in reverse order, except this time they're forward. That reversal twist is what kills candidates who memorize the first version. Juniper Networks has asked this one. The trap is assuming you can just walk both lists head-to-head and add digits. You can't. You need to handle the carry, handle different list lengths, and you need to know which data structure lets you process from the back. If this lands in your assessment and you blank on the stack approach, StealthCoder surfaces the solution invisible to the proctor.
Companies that ask "Add Two Numbers II"
Add Two Numbers II 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. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too.
Get StealthCoderThe core trick: you can't add numbers forward without knowing future carries. Stack both lists, pop from the back, build your result in reverse, then reverse again to get the answer in the right order. The gotcha is that many people try to reverse the lists themselves, which works but costs extra passes and confuses the logic. A stack-based approach is cleaner. The math part is straightforward once you accept that you're processing digit by digit with carry propagation. Common failure: forgetting the final carry after both lists are exhausted, or not reversing your result before returning it. Linked List and Stack are both in the topic set here, and this problem forces you to use both. If you've drilled the original Add Two Numbers, your instinct is wrong for this one, which is exactly why it's a favorite.
Pattern tags
You know the problem.
Make sure you actually pass it.
Add Two Numbers II 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. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Add Two Numbers II interview FAQ
How is this different from the original Add Two Numbers problem?+
In the original, lists are in reverse order (units digit first). Here they're forward (most significant digit first). That means you can't just walk head-to-head adding digits. You need a way to access digits from the back, which is why Stack is listed as a topic. The carry logic also depends on knowing future digits, so the problem forces a different approach.
Do I have to use a stack?+
Not technically. You can reverse both lists, add them, then reverse the result. But a stack solution is cleaner and shows you understand the data structure's purpose. The stack approach is what gets hired candidates through when they've only half-prepped.
What's the trick to handling the final carry?+
After both stacks are empty, check if carry is still nonzero. If it is, create one more node. It's a small detail but it's the line that separates a passing solution from one that fails on edge cases.
Is this problem still asked at real companies?+
Juniper Networks has asked it according to reports. It's not as ubiquitous as some linked list problems, but it appears frequently enough that skipping it is risky if you're interviewing at companies that do heavy systems or networking work.
How hard is a 61% acceptance rate for a medium?+
That's below average for a medium. Most people miss the stack insight or mess up the reversal logic. If you know the pattern, it's straightforward. If you don't, you'll waste time trying to brute force. That gap is where StealthCoder saves your OA.
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