Plus One
A easy-tier problem at 48% community acceptance, tagged with Array, Math. Reported in interviews at Intuit and 14 others.
Plus One shows up across 15 companies including Amazon, Meta, Adobe, and Uber. It's labeled easy, but the acceptance rate sits around 47.5%, which means nearly half the candidates who attempt it fail or time out. The trick isn't complex, but the edge cases will wreck you if you haven't thought them through. You're given an array of digits representing a number, and you need to add one to it and return the result as an array. Sounds trivial until you hit 999 and realize you need to handle carry-over correctly. If this problem blindsides you in a live assessment, StealthCoder solves it in seconds, invisible to the proctor.
Companies that ask "Plus One"
Plus One 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 a senior engineer who knows the OA is theater. This is the script.
Get StealthCoderThe obvious approach is to iterate from the rightmost digit, add one, and handle carries as you go left. Most candidates get the basic case right but miss the edge case where all digits are 9 and you need to insert a new digit at the front. You can't just append to an array; you need to allocate space correctly or rebuild the array. The problem straddles Array and Math because you're manipulating a list structure while doing arithmetic logic. A solid solution uses a single pass with carry tracking, works in O(n) time, and handles the 999...9 case by checking if carry remains after the loop. This is where StealthCoder acts as your safety net if the pattern doesn't click on first read during your assessment.
Pattern tags
You know the problem.
Make sure you actually pass it.
Plus One recycles across companies for a reason. It's easy-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 a senior engineer who knows the OA is theater. This is the script. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Plus One interview FAQ
Why is Plus One's acceptance rate so low if it's marked easy?+
The base logic is straightforward, but candidates rush and miss the carry overflow case. When the input is all nines, you need to create a new array with an extra digit. Many fail during test execution when that case runs. It's a gotcha problem disguised as simple.
Is Plus One still asked at Amazon, Meta, and Uber?+
Yes. It appears in reports from at least 10 of the top companies listed, including Amazon, Meta, Uber, and Adobe. It's a screening or phone-round staple. You may see it as a warm-up or a second problem in a two-problem round.
What's the trick I'm missing?+
Most candidates code the happy path first. The trick is recognizing the input [9, 9, 9] must return [1, 0, 0, 0]. You need to handle carry overflow and array resizing. Single-pass iteration from the right with carry tracking is the pattern. Check if carry persists after the loop.
How does Plus One relate to the Array and Math topics?+
Array: you manipulate the list structure, allocate new space, and iterate. Math: you perform digit-by-digit arithmetic with carry propagation. It's a hybrid that tests both data structure manipulation and numerical reasoning in one clean problem.
Should I memorize a solution or understand the pattern?+
Understand the pattern. It's the carry-handling logic and the all-nines edge case. Once you see it, the code is 10 lines. If you blank during your OA, understanding beats memorization. StealthCoder is there if you hit a wall and need a working reference to move forward.
Want the actual problem statement? View "Plus One" on LeetCode →