← Bytedance Interview Insights
Backtracking problem, classic but still annoying under pressure.
Start by clarifying the problem (e.g., return all solutions or count). Then present a backtracking solution with pruning using sets for columns and diagonals, and analyze time complexity as O(N!) with O(N) space.
Pro tip: Mention that while the theoretical upper bound is O(N!), pruning makes it much faster in practice; for N=8, it explores only ~15,000 nodes instead of 16 million.
Ask whether to return all distinct solutions or just the count, and confirm the input range. This shows attention to detail and avoids solving the wrong problem.
Explain that you'll place queens row by row, using sets to track occupied columns and diagonals. At each row, try each column and recurse if safe.
Write clean code with helper functions for safety checks. Use bit manipulation or boolean arrays for O(1) checks, and mention symmetry reduction if needed.
Derive the worst-case time complexity as O(N!) because in the first row there are N choices, then at most N-1, etc. Space is O(N) for recursion and sets.
Mention that the actual runtime is much better due to pruning, and briefly discuss alternative approaches like genetic algorithms or constraint programming for large N.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.