Lucky Numbers in a Matrix
A easy-tier problem at 80% community acceptance, tagged with Array, Matrix. Reported in interviews at Cisco and 0 others.
Lucky Numbers in a Matrix is an easy problem that shows up in Cisco interviews and tests whether you can read a matrix correctly under pressure. With a 79% acceptance rate, it's one of those deceptive problems where the trick isn't algorithmic complexity but understanding what the problem actually asks. Most candidates fail by overthinking it or misreading the definition of a lucky number. If this problem hits your live assessment and you blank on the exact condition, StealthCoder surfaces the solution in seconds, invisible to the proctor.
Companies that ask "Lucky Numbers in a Matrix"
Lucky Numbers in a Matrix 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 StealthCoderA lucky number in a matrix is an element that is the minimum in its row AND the maximum in its column simultaneously. The catch is that candidates often reverse the condition or only check one dimension. The straightforward approach is to precompute row minimums and column maximums, then iterate the matrix once more to find elements that satisfy both. This takes O(m*n) time and O(m+n) space. The problem isn't hard algorithmically, but reading comprehension and careful validation matter in a live OA where you're nervous. StealthCoder is the hedge for when you misread the definition under time pressure and need the exact condition confirmed.
Pattern tags
You know the problem.
Make sure you actually pass it.
Lucky Numbers in a Matrix 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.
Lucky Numbers in a Matrix interview FAQ
Is Lucky Numbers in a Matrix still asked at major companies?+
Yes. It appears in Cisco's interview loop. The low difficulty makes it a screening question, so it's asked frequently but usually early. The real test is clean implementation and reading comprehension, not algorithmic insight.
What's the most common mistake candidates make?+
Reversing the condition: checking if the element is the maximum in its row and minimum in its column, not the other way around. Others iterate only rows or only columns and miss lucky numbers entirely. Careful re-reading of the problem statement before coding saves 90% of failures.
Can I solve this without precomputing row and column extremes?+
Technically yes, but it's slower. Nested loops checking each element against all others in its row and column work but invite off-by-one errors and are O(m*n^2) worst case. Precomputing row mins and column maxs first is cleaner and faster, and easier to validate in a live setting.
How does this problem relate to the Matrix and Array topics?+
It tests basic 2D array iteration and multi-dimensional indexing. You need to track state across rows and columns simultaneously, which is the core of matrix problems. It's a stepping stone to harder problems that require more complex traversal patterns.
Is there a trick to spotting lucky numbers faster?+
No mathematical shortcut exists. The only optimization is ensuring your row-min and column-max lookup is O(1) via a hash or pre-filled structure. In a live OA, write the straightforward two-pass solution and verify the logic before submitting.
Want the actual problem statement? View "Lucky Numbers in a Matrix" on LeetCode →