Overview
Sharing my Round 1 technical screening experience for a Staff Software Engineer role at Tekion. The interviewer picked variations of well-known problems and cared about the underlying insight, not just brute-force code.
Round 1 — Technical Screening
Problem 1: 100 Lockers (variation of Bulb Switcher)
You're in a hallway with 100 closed lockers.
- Open every locker (pass 1)
- Close every 2nd locker (pass 2)
- Toggle every 3rd locker (pass 3)
- ...continue for 100 passes
How many lockers are open at the end?
The interviewer wanted the insight: a locker is toggled once per divisor, so it ends open only if it has an odd number of divisors — which happens only for perfect squares. Answer: 10 (the perfect squares 1, 4, 9, ..., 100).
Problem 2: Coin Game (variation of Stone Game)
Two players, A and B, alternate turns. A row with an even number of coins. On each turn, a player takes a coin from either the left or right corner. The player with more total value wins. A (younger) goes first, both play optimally.
This is a minimax DP problem: dp[i][j] = best score the current player can achieve on the subarray. There's also a neat result — with an even number of coins, the first player can always guarantee a win or tie using the odd/even index sum trick.
Takeaways
- Staff-level screening uses "simple" problems with depth — the interviewer cares about the mathematical/algorithmic insight, not just a working simulation.
- Know the classics and their variations — Bulb Switcher, Stone Game, and their reframings show up often.
- Explain the "why" — for the lockers, articulate why only perfect squares stay open. For the coin game, explain the optimal-play reasoning.
Prep Recommendation
- Number theory basics (divisors, perfect squares)
- Game theory DP (minimax, interval DP like Stone Game / Predict the Winner)
- Practice explaining the insight clearly — at Staff level, communication of reasoning matters as much as the solution.