Meeting Rooms: the idea to remember.

The core insight

Sort meetings by start and compare each start to the previous end.

Why it works

If any two sorted intervals overlap, the first conflict is visible between adjacent intervals; without adjacent conflicts the whole schedule is compatible.

The mistake to avoid

Use start < previousEnd for a conflict. Equality is allowed.

Commented Java solution

Use java.util.* imports and a surrounding solution class. Tree snippets assume the standard TreeNode definition; linked lists use ListNode and Clone Graph uses a Node with val and neighbors; Copy Random List uses Node with val, next and random. Read the input assumptions above.

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

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