Blind 75Easy

Meeting Rooms — Sort and Check Overlaps

Sort intervals by start time and ensure each meeting starts after the previous one ends.

IntervalSorting

View problem on LeetCode

Problem Statement

Determine if a person could attend all meetings given start-end intervals.

Why This Problem Matters

Simpler precursor to Meeting Rooms II.
Tests interval sorting and overlap detection.
Appears frequently as a warm-up in interviews.

Thought Process

Sort by start time

Ordering makes it easy to compare each meeting against the previous one.

Check for overlaps

If current.start < previous.end, meetings conflict.

Return true when all non-overlapping

After loop, if no conflicts found, all meetings are attendable.

Step-by-Step Reasoning

Sort intervals by start.
Iterate i from 1..n-1; if intervals[i][0] < intervals[i-1][1], return false.
Return true after loop completes.

Dry Run

[[0,30],[5,10],[15,20]]

Overlap detected since 5 < 30; return false.

[[7,10],[2,4]]

No overlaps; return true.

Complexity Analysis

Time

O(n log n)

Space

O(1)

Why

Sorting dominates; comparisons are linear.

Annotated Solution

JAVA

import java.util.Arrays;

public class MeetingRooms {
  public boolean canAttendMeetings(int[][] intervals) {
    Arrays.sort(intervals, (a, b) -> Integer.compare(a[0], b[0]));
    for (int i = 1; i < intervals.length; i += 1) {
      if (intervals[i][0] < intervals[i - 1][1]) {
        return false;
      }
    }
    return true;
  }
}

Sorting ensures only adjacent intervals need comparison, keeping logic simple.

Common Pitfalls

Skipping sort leads to incorrect comparisons.
Using <= instead of < treats back-to-back meetings as conflict; confirm requirement with interviewer.
Returning after first non-overlap misses later conflicts—ensure loop continues.

Follow-Up Questions

How would you return the maximum number of meetings that can be attended? (Interval scheduling.)
Can you handle meeting priorities or weights?

Key Takeaways

Sorting is often the first step in interval problems.

Clarify whether touching meetings conflict to choose < vs <=.

Meeting Rooms II builds directly on this logic—be ready to discuss.