FAANG · LeetCode #252

Meeting Rooms — three-stage drill

1The ProblemEasy

Meeting Rooms

Can one person attend every meeting? — any overlap means no.

Examples

[[0,30],[5,10],[15,20]]→ false[[7,10],[2,4]]→ true

constraintMeetings are half-open intervals [start, end); a meeting ending at t and another starting at t do NOT overlap.

2The PatternTIME O(n log n) · SPACE O(n)

Intervals

Given a pile of ranges, sort them by start — now any overlap is a neighbour, so a single left→right pass handles them.

Problems using this pattern

3The SolutionRESULT → true

Step through it

given: 3 meetings · can one person attend all of them?

Step 1 / 5

Python▎sort · sweep · clash → false

1def canAttendMeetings(intervals):
2    intervals.sort(key=lambda iv: iv[0])
3    for i in range(1, len(intervals)):
4        if intervals[i][0] < intervals[i - 1][1]:
5            return False
6    return True

why it worksSort by start, then one left→right pass: for each meeting, check that its start is ≥ the previous meeting's end. The moment it isn't, return false. Sorting makes overlaps strictly local — you only ever have to compare to the immediate predecessor. O(n log n) for the sort, O(n) for the sweep.

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Shortest Subarray with Sum at Least K

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Intervals

Meeting Rooms — three-stage drill

Meeting Rooms

Intervals

Step through it

All problems by pattern

Two Pointers

Sliding Window

Prefix Sum

Monotonic Deque

Binary Search

Arrays & Hashing

Monotonic Stack

Intervals

Heap / Top-K

Backtracking

Recursive Descent