Hi since I didn’t see a discussion thread for ZCO this year, I decided to make one. Discuss answers/everything else here (I didn’t give ZCO myself though).
Q1 (Vacation) was a pretty clear application of 2D prefix sums, though I wasted some time in the implementation thanks to annoying typos
Q2 (Messages) really stumped me, I made a brute force-ish solution (with binary encoding to optimize it a little) and got 3 subtasks. I wrote a new solution for the next 2 subtasks, but had no idea for the full solution, ending up with 164 total.
If you got 142, then I think you passed the first 3 subtasks, which is where I basically converted the binary string of differences between two messages into an integer to handle checking from 0 to 2^N - 1 in a easier way