Hey guys! I just finished the Remove K Digits problem, and my initial answer used concatenation to create the output String. I recieved a time of 43ms, which was quite slow compared to other submissions, so I went to the discussion section to see how I could make it faster. I noticed that others used StringBuilder rather than concatenation. I had also seen StringBuilder be used on other problems in the past. Anyways, I decided to take a look at the SB Class. It decreased the runtime from 43 ms to 6 ms. I'm not sure if this is a nooby question, but I'd appreciate it if someone could simply explain why StringBuilder resulted in a much shorter runtime.