My solutions written in C# - they are not necessarily the optimal solutions, nor are they necessarily particularly well written, as long as they give the correct answer, they're good enough for me. I am solving every day using no non-standard libraries and with as minimal help as possible, but am not necessarily going for the fastest times.
I am not including my puzzle input with the solutions, as they should work with anyone's (it looks for it in files named input01.txt and onwards in the same folder as the .cs source files).
Each day's class is designed to be entirely independent from the others and have no external dependencies, so some common methods, like the mod function, may be defined multiple times.