I'm sure it's simple if you know it! But having not taking an algorithm class before, and having completed three other Algorithm questions within the 90 min tot

I'm sure it's simple if you know it! But having not taking an algorithm class before, and having completed three other Algorithm questions within the 90 min total allotted time, I crashed pretty hard. I solved it afterwards when I had time to really think, but didn't know it off the top of my head.