Given time intervals, find the minimum number of conference rooms required
The code looks much simpler than I would expect for this task. I tried several examples but could neither make it fail, nor did I understand why and how this algorithm works, I was only delighted that it seems to work. Therefore I have only a few remarks.

The early return for length &lt;= 1 is not necessary.

The ++rooms is missing the semicolon.

Apart from that, it looks perfect.