Meeting Rooms I - Algorithm

Algorithm: Sort by start time. Check if any meeting starts before the previous one ends.

function canAttendMeetings(intervals)
 sort intervals by start time ascending
 for i from 1 to length of intervals - 1
 if intervals[i].start < intervals[i-1].end then
 return false
 return true

Time: $O(n \log n)$. Space: $O(1)$ extra.