Combine date ranges in PHP

I need to get data for specified date ranges. Some date ranges overlap which causes getting overlapping data. I need the script to take date ranges and return date ranges that do not overlap. Input: $range[1][start] = strtotime ("2009-01-07 15:22:22"); $range[1][end] = strtotime ("2009-01-07 15:22:22"); $range[2][start] = strtotime ("2009-01-06 15:22:22"); $range[2][end] = strtotime ("2009-01-09 16:22:22"); $range[3][start] = strtotime ("2008-12-06 15:22:22"); $range[3][end] = strtotime ("2009-01-07 15:22:22"); The output shpuld return date ranges that do not overlap: (For this example, there would be just one range outputted) $out[0][start] = strtotime ("2008-12-06 15:22:22"); $out[0][end] = strtotime ("2009-01-09 16:22:22"); The script needs to be very efficient, no garbage. I need the developer to start as soon as I pick him/her.