Advent of Code 2017

This directory contains my solutions to the 25-day Advent of Code 2017. I'll be trying to solve as many as I can in Swift 4, but if I run into trouble I may switch to some other language. My plan is for each day to have its own subdirectory, containing these files:

• part1-problem.md, part2-problem.md. Descriptions of the day's two puzzles (Part 1 and Part 2), copied from the AoC website. The way it works is, Part 2 is a twist on Part 1 that is disclosed after you've entered the correct answer to Part 1.
• main.swift. My solution logic, in the form of a solve1() function for Part 1 and a solve2() function for Part 2. If the code gets big and unwieldy I'll split it across additional .swift files. The main logic, though, must be in main.swift, and I expect to always use functions called solve1() and solve2().
• input.swift. The input data, in the form of a global string array variable called inputLines. The same input data is used for both Part 1 and Part 2. Different AoC users get different input data, so if you explore other people's AoC repositories their input will likely not match mine.
• answers.swift. String variables containing the correct answers for Part 1 and Part 2, assuming I'm able to find them out by solving the day's puzzles. I figure at some point I might want to set up some kind of automated regression testing.
• README.md (optional). I'm thinking this could be a place for general discussion of obstacles I encountered and things I learned. I may or may not get around to creating this file for any given day.

My AoC code usually starts quick and dirty. In particular, I'll often start Part 2 by copy-pasting the solve1() code into solve2(). To varying degrees I will come back and clean the code up, but my priority will be whatever it takes to get the correct answer as fast as I can.

I've been using CodeRunner to code, run, and debug these programs. [Update: I've switched to Xcode for Swift coding. More about this in my Day 3 notes.] If you don't have CodeRunner you can run them from the command line, after cd-ing to that day's directory:

# Swift
swiftc -o main *.swift && ./main

# Python
python MyFile.py

# Objective-C
xcrun clang -fobjc-arc -framework Foundation -ObjC -o MyFile.out MyFile.m
MyFile.out

TODO: Add instructions for running Java from the command line. Add instructions for using homebrew to install Java (my preference).

TODO: Figure out how to invoke the debugger from the command line, and add instructions here.

Links on the AoC website look like this:

• Problem description: http://adventofcode.com/2017/day/1.
• Input data: http://adventofcode.com/2017/day/1/input.

Tips

TODO: Add notes on AoC in general, how it works, more tips.

• Beware accidental add trailing newlines in the input.txt files.
  • In Python, can strip trailing newlines before splitting the file into lines:

     return [line.rstrip('\n') for line in open(filePath)]

  • In Swift, can use where as a loop condition:

     for line in lines where !line.isEmpty {