Day 7 solution

Cleaned this one up a bit after getting the solve, and did a few things to make Rider quiet.

src/07.cs

@@ -0,0 +1,116 @@
+namespace aoc2022;
+
+internal class Day07 : Day
+{
+    private class file
+    {
+        public long size;
+        // ReSharper disable once NotAccessedField.Local
+        public string name = string.Empty;
+
+        public override string ToString() => $"{name}, {size:N0}b";
+    }
+
+    private class dir
+    {
+        public dir? outer;
+        public readonly List<dir> dirs = new();
+        public readonly List<file> files = new();
+        public string name = string.Empty;
+
+        public long size => files.Sum(x => x.size) + dirs.Sum(x => x.size);
+
+        public override string ToString() => $"{name}, {size:N0}b, {dirs.Count} dir{(dirs.Count == 1 ? "" : "s")}, {files.Count} file{(files.Count == 1 ? "" : "s")}{(outer != null ? $", parent '{outer.name}'" : "")}";
+    }
+
+    private readonly dir rootDir = new() {name = "/"};
+
+    internal override void Parse()
+    {
+        dir? curr = null;
+
+        foreach (var line in Util.ReadAllLines("07"))
+        {
+            if (line.StartsWith("$"))
+            {
+                var cmd = line[2..];
+                string? arg = null;
+                if (cmd.Contains(' '))
+                {
+                    arg = cmd[(cmd.IndexOf(' ') + 1)..];
+                    cmd = cmd[..cmd.IndexOf(' ')];
+                }
+
+                if (cmd == "cd")
+                {
+                    if (arg == "/")
+                    {
+                        curr = rootDir;
+                    }
+                    else if (arg == "..")
+                    {
+                        curr = curr!.outer;
+                    }
+                    else
+                    {
+                        curr = curr!.dirs.First(x => x.name == arg);
+                    }
+                }
+            }
+            else
+            {
+                var parts = line.Split(' ');
+                if (parts[0] == "dir")
+                {
+                    curr!.dirs.Add(new dir() { name = parts[1], outer = curr });
+                }
+                else
+                {
+                    curr!.files.Add(new file { size = long.Parse(parts[0]), name = parts[1] });
+                }
+            }
+        }
+    }
+
+    private static IEnumerable<dir> GetCandidates(dir root, long? threshold = null)
+    {
+        if (threshold == null || root.size <= threshold)
+        {
+            yield return root;
+        }
+
+        foreach (var dir in root.dirs)
+        {
+            if (threshold == null || dir.size <= threshold)
+            {
+                yield return dir;
+            }
+
+            foreach (var d in dir.dirs.SelectMany(d2 => GetCandidates(d2, threshold)))
+            {
+                yield return d;
+            }
+        }
+    }
+
+    internal override string Part1()
+    {
+        List<dir> candidates = new(GetCandidates(rootDir, 100000));
+
+        return $"Sum of directories below 100,000 bytes: <+white>{candidates.Sum(x => x.size)}";
+    }
+
+    internal override string Part2()
+    {
+        List<dir> flatDirList = new(GetCandidates(rootDir));
+        var rootSize = rootDir.size;
+        const int totalSize = 70000000;
+        var currentFreeSpace = totalSize - rootSize;
+        const int totalNeededFreeSpace = 30000000;
+        var neededFreeSpace = totalNeededFreeSpace - currentFreeSpace;
+
+        var smallestCandidate = flatDirList.Where(x => x.size >= neededFreeSpace).MinBy(x => x.size);
+
+        return $"Smallest directory that can free the required {neededFreeSpace:N0} bytes: <+white>{smallestCandidate!.size}";
+    }
+}