Date: 2026-06-06
Time: 18:22
This file implements LeetCode problem #1450, "Number of Students Doing Homework at a Given Time." It's a self-contained solution + test module — one of hundreds in the leetcode-implementations repo, each following the same solution.py + test_solution.py structure (though here both are combined in a single file).
The responsibility is narrow: given parallel arrays of student start/end times, count how many students are actively working at a specific query time.
Solution.busyStudent (line 9) — The core method. Takes three arguments:
startTime: List[int] — per-student homework start timesendTime: List[int] — per-student homework end times (parallel to startTime)queryTime: int — the instant to checkReturns the count of students where startTime[i] <= queryTime <= endTime[i]. The contract assumes startTime and endTime are the same length (LeetCode guarantees this).
TestBusyStudent (line 22) — Seven test cases covering the standard examples, all-busy, none-busy, and boundary conditions (query exactly at start, exactly at end, just outside both ends).
sum(1 for ... if ...) is a common Python idiom for counting matches without materializing a list. O(n) time, O(1) auxiliary space.s <= queryTime <= e uses Python's chained comparison syntax — equivalent to s <= queryTime and queryTime <= e but more readable and evaluated left-to-right with short-circuit.zip: The problem gives two parallel lists; zip(startTime, endTime) pairs them element-wise, which is the idiomatic way to traverse correlated sequences.Solution class and unittest.TestCase subclass, guarded by if _name == "main". A separate testsolution.py exists alongside it for the test harness.Imports: unittest (stdlib), typing.List (type annotation only — no runtime effect).
Imported by: The "Imported By" list is misleadingly large — those 300+ testsolution.py files likely share a common test runner (runtests.py at the repo root) rather than directly importing this module. The actual dependent is number-of-students-doing-homework-at-a-given-time/test_solution.py.
1. Caller passes two equal-length lists and a scalar query time.
2. zip pairs the i-th start with the i-th end time.
3. The generator checks each pair against the chained inequality.
4. sum counts the 1s (truthy matches), returning the total.
Single pass, no intermediate data structures.
startTime and endTime must be equal length — the code doesn't validate this; it relies on LeetCode's problem constraints.queryTime=5 and queryTime=10. The boundary tests at lines 37-41 verify this explicitly.None. Empty inputs produce 0 naturally (sum of an empty generator is 0). Mismatched list lengths would silently truncate to the shorter list via zip behavior — no error raised.
number-of-students-doing-homework-at-a-given-time/test_solution.py — The separate test file; compare how it differs from the inline tests hererun_tests.py — The repo-wide test harness that drives all solution testsdetermine-if-two-events-have-conflict/solution.py:Solution — Another interval-overlap problem; compare the range-check patternnumber-of-students-doing-homework-at-a-given-time/review.md — The code review notes for this solutionzip-truncation-behavior — Python's zip silently drops excess elements from the longer iterable; relevant if input invariants ever breakbusyStudent-inclusive-boundaries — busyStudent counts a student as busy when queryTime equals exactly startTime[i] or exactly endTime[i] (inclusive on both ends)busyStudent-linear-constant-space — The solution runs in O(n) time and O(1) auxiliary space via a generator expression, never materializing an intermediate listbusyStudent-empty-input-safe — Passing empty lists for startTime and endTime returns 0 without error, because sum of an empty generator is 0busyStudent-no-input-validation — The method does not validate that startTime and endTime have equal length; mismatched lengths silently truncate via zip