Of course I ended up with a off-by-one error for the second part, so things took a bit longer than they really should've.
But either way, behold, messy C#:
C#
int[][] reports = new int[0][];
public void Input(IEnumerable<string> lines)
{
reports = lines.Select(l => l.Split(' ').Select(p => int.Parse(p)).ToArray()).ToArray();
}
public void Part1()
{
int safeCount = reports.Where(report => CheckReport(report)).Count();
Console.WriteLine($"Safe: {safeCount}");
}
public void Part2()
{
int safeCount = reports.Where(report => {
if (CheckReport(report))
return true;
for (int i = 0; i < report.Length; ++i)
if (CheckReport(report.Where((_, j) => j != i)))
return true;
return false;
}).Count();
Console.WriteLine($"Safe: {safeCount}");
}
bool CheckReport(IEnumerable<int> report)
{
var diffs = report.SkipLast(1).Zip(report.Skip(1)).Select(v => v.Second - v.First);
return diffs.All(v => Math.Abs(v) <= 3) && (diffs.All(v => v > 0) || diffs.All(v => v < 0));
}