193. Meeting Rooms

After sorting meetings by start time, the only possible conflicts are between consecutive meetings. If any meeting starts before the previous one ends, they overlap.

Why adjacent-only

Sort the intervals by start time. Now they appear in chronological order, so a meeting can only clash with the one immediately before it — if it started before an earlier meeting, sorting would have placed it earlier. Thus a single left-to-right pass suffices.

intervals.sort()
for i in 1..n-1:
    if intervals[i].start < intervals[i-1].end: return False
return True

Note end == start is allowed (back-to-back meetings don't overlap).

Worked example

[[0,30],[5,10],[15,20]] sorted stays the same: 5 < 30 → overlap → false.

Complexity

• Time: O(n log n) for the sort.
• Space: O(1) extra (or O(n) for the sort).

import java.util.Arrays;

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