Interval Usage with Non-Overlapping Overrides
Reported by candidates from Crusoe's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
You've got a Crusoe OA arriving in May with an interval precedence problem. You're given usage intervals (default state) and non-overlapping override intervals (forced state). The trap is thinking day-by-day: that's O(D), which they'll reject. The real pattern is event-based: sweep through interval endpoints, track active usage intervals, and flip state only when overrides kick in or usage changes. You need to output a binary string for each day 1 to D. StealthCoder will catch the logic if you blank on the sweep-line approach.
The problem
Complete the function below. The function receives the full standard input as a single string and must return the exact standard output lines for the described problem. Problem You are given a timeline of days ([1..D]) and two kinds of interval events: Usage intervals: indicate whether a resource is in-use during that period. Override intervals: override the final state during that period. Override intervals do not overlap each other. Clarified FastPrep contract A day is in use by default if at least one usage interval with value 1 covers that day. Usage intervals with value 0 do not clear another usage interval; they simply contribute no usage. Override intervals are the only intervals that force the final state to their value, and override intervals never overlap each other. Rules: By default, a day's state is determined by the union/combination of usage intervals. If a day falls within an override interval, the override value takes precedence over usage. Implement an algorithm to output the final state for each day from 1 to D. Input (stdin) Line 1: integer D. Line 2: integer U. Next U lines: l r v describing a usage interval ([l,r]) (inclusive), with v in {0,1}. Next line: integer O. Next O lines: l r v describing an override interval ([l,r]) (inclusive), with v in {0,1}. Override intervals never overlap. Output (stdout) One line: a string of length D over {'0','1'}, where the i-th char is the final state on day i. Complexity Preferably better than day-by-day simulation; e.g. O((U+O) log (U+O) + D). Example See tests below. Example Input 10 2 1 2 1 4 10 1 1 2 4 0 Output 1000111111 Function Description Complete solveIntervalUsageWithOverrides. It has one parameter, String input, containing the full stdin payload. Return the stdout payload as an array of lines, without trailing newline characters. The returned string array must match the expected standard output lines for the sample input.Reported by candidates. Source: FastPrep
Pattern and pitfall
This is a classic interval merging + precedence problem disguised as a timeline question. Build a list of events at each interval boundary (start, end). Process events in order, maintaining a count of active usage-1 intervals. For each position, check if an override covers it (overrides take absolute precedence). If no override, the day is '1' if any usage-1 interval is active, else '0'. The key insight: you don't iterate days; you iterate interval endpoints. Complexity is O((U+O) log(U+O)) for sorting plus O(D) to output. Common mistake: treating usage-0 intervals as active negation instead of no-ops. Overrides are atomic; they never overlap, so no conflict resolution. StealthCoder handles the event sweep if you freeze on the data structure.
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You can drill Interval Usage with Non-Overlapping Overrides cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Built by an Amazon engineer who passed his OA cold and still thinks the filter is broken.
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Interval Usage with Non-Overlapping Overrides FAQ
Do usage-0 intervals clear previous usage-1 intervals on the same day?+
No. Usage-0 intervals are no-ops; they don't negate or clear. A day is in-use if at least one usage-1 interval covers it. Multiple usage-1 intervals on the same day still result in state '1'.
What happens if an override interval overlaps multiple usage intervals?+
The override takes absolute precedence. Whatever the usage intervals say, the override value is the final state for every day in that override range. Usage intervals underneath don't matter.
Can I simulate day-by-day and check each interval for each day?+
Technically yes, but they hint at O((U+O) log(U+O) + D), not O(D*U). That means event-based processing: sort interval endpoints, sweep left-to-right, track active usage counts, and output each day in one pass.
How do I handle override intervals that straddle usage interval boundaries?+
Overrides are independent. Process them separately. For each day, check if an override covers it first. If yes, output the override value. If no, output the OR of all usage-1 intervals on that day.
Is this a segment tree or do I really need event-based sweep?+
Event sweep is sufficient and matches the hinted complexity. Parse all U+O intervals, create events at each start/end, sort, then iterate days and check which events are active. Segment trees are overkill here.