I spent 6 weeks doing Leetcode problems, mostly medium-level ones. However when the take-home project was assigned, my submittal crashed on their end, even though it ran on my end on two different simulators and my phone! That pretty much canned my application there and then, even though the engineer agreed with me that the crash was VERY weird... it involved iOS crashing while adding a valid string to a Set, which was non-null! Given the opportunity, I could have quickly changed the Set usage to an Array, but that wasn't put on the table. In other words, a real-world fix didn't make sense to them!