I knew this one but still fumbled the two-pointer approach explaining it out loud.
Start by clarifying the problem and walking through a small example to confirm understanding. Then explain the brute-force approach and optimize it using precomputed left and right maximum arrays or a two-pointer technique, discussing time and space complexity trade-offs. Finally, code the solution cleanly and test with edge cases.
Pro tip: At Meta, interviewers value clear communication and iterative improvement. Begin with a straightforward solution, then optimize while explaining your thought process—this demonstrates problem-solving skills and collaboration.
Restate the problem in your own words and ask clarifying questions about input constraints, edge cases, and expected output format.
Walk through a small example manually to verify your understanding and identify patterns, such as water trapped at each index depends on the minimum of the maximum heights to its left and right.
Present a brute-force solution first, then propose optimizations like precomputing left/right max arrays (O(n) time, O(n) space) or using two pointers (O(n) time, O(1) space).
Write clean code for the chosen approach, then test with edge cases like empty array, single bar, increasing/decreasing heights, and flat terrain.
State the time and space complexity of your solution and discuss potential trade-offs or further optimizations.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.