I competed in the Crash and Compile qualifications at DEF CON this year. Looks like they haven't yet published the problems on their Past Content page yet, but I figured I'd throw my solutions up on GitHub just for posterity.
I worked on the Contact problems while my partner (@jmaggio14) worked on the Locate problems. I managed to get the Easy one solved and submitted pretty quickly, but got completely stumped by the Medium problem for a while. I then switched to the Hard problem, which I managed to figure out in not too much time. Unfortunately, the actual implementation I wrote for it got really convoluted really fast, and I ran out of time trying to debug it. :(
Ultimately, we only had Contact-Easy successfully submitted (Jeff got Locate-Easy solved but was seconds late on the upload), so we only made it as an alternate team for the actual competition (and everyone showed up, so we didn't get to compete). Welp, nothing to do but try again next year!