Array Formula: my problem for some help

Hello,

Please find attached a sample copy of the spreadsheet I'm working with.

In it, you'll see 4 columns. The first 3, Classroom, Start, and End, are my knowns. The last column, I'd like to create a formula to solve for either TRUE or FALSE based on the other columns. The cell should return TRUE if the Start and End times conflict with another Start and End time for the same Classroom, and FALSE if there are no conflicts.

I think you need to use an array formula to make it work, but since I'm so bad with those, I thought I might post my problem for some help. Any and all help would be greatly appreciated!

Thank you so much in advance

John

If I've understood...

D2:
=IF(COUNTIF($A$2:$A$5,$A2)=1,FALSE,SUMPRODUCT(--($A$2:$A$5=$A2),--(ROW($A$2:$A$5)<>ROW()),SIGN((($B$2:$B$5>=$B2)*($B$2:$B$5<=$C2))+(($C$2:$C$5>=$B2)*($C$2:$C$5<=$C2))+(($B$2:$B$5<=$B2)*($C$2:$C$5>=$C2))))>0)
copied down

on large datasets the above will not perform well however... SUMPRODUCT (like an Array) is pretty inefficient.