Range Addition II
A easy-tier problem at 57% community acceptance, tagged with Array, Math. Reported in interviews at IXL and 0 others.
Range Addition II looks simple on the surface, but the naive simulation approach will TLE you if you're not careful about the constraint. IXL asks this, and candidates often burn time building a full matrix when the real insight is pure math. The problem hands you a series of range increments on a 2D grid and asks you to count cells with the maximum value. Most people implement the obvious O(m*n*k) brute force. The trick is recognizing that you don't need to track the grid at all, you only care about the rectangle that gets incremented by all operations. If you blank on the optimization during your OA, StealthCoder surfaces the math-first solution in seconds, invisible to the proctor.
Companies that ask "Range Addition II"
Range Addition 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 for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe catch here is that candidates default to simulation: create the grid, apply each operation, find the max. That's slow. The real pattern is overlap geometry. Every operation increments a rectangle from (0,0) to (a_i, b_i). The cells with the maximum value are exactly those covered by ALL operations, the intersection of every rectangle. That intersection is a single rectangle with dimensions (min(a_i), min(b_i)). Your answer is just that product. The topics listed, Array and Math, reflect this duality: you're given an array of operations but the solution is pure arithmetic. Common miss: trying to build the matrix or trace every cell. The hedge: if you're unsure during the live assessment, StealthCoder runs invisibly and gives you the O(k) math solution so you move on.
Pattern tags
You know the problem.
Make sure you actually pass it.
Range Addition II 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. Made for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Range Addition II interview FAQ
Why does the brute-force grid simulation fail here?+
Because you're iterating every operation and every cell in each rectangle, which is O(m*n*k) where k is the operation count. On large grids with many operations, that's too slow. The acceptance rate here is 57%, partly because candidates don't spot the math shortcut and TLE on simulation.
What's the actual insight to solve this efficiently?+
You don't need the grid. Only cells covered by all operations hit the max. That's the intersection of all rectangles, which is one smaller rectangle with width min(a_i) and height min(b_i). Answer is just that product. Time is O(k), space is O(1).
Does IXL ask follow-ups or harder variants of this?+
IXL is the only company on record for this problem, and it's rated Easy. Expect the core problem as stated. No variant data available, so assume the problem as written is the full scope of the question.
How do I avoid the 'build the matrix' trap during the interview?+
Read the constraints first. If m, n, and k are all large, simulation is a red flag. Ask yourself: 'Do I actually need to store the grid?' Here, the answer is no. Think about what the question really wants: max value count, not the grid itself.
Is this problem still asked at tech companies?+
IXL reports asking it, and it's categorized as Easy with a 57% acceptance rate, suggesting it's still live. It's a good warm-up or filter question. Don't expect it to be asked at every company, but if it lands in your OA, the math trick is non-negotiable.
Want the actual problem statement? View "Range Addition II" on LeetCode →