#define Day12
#if Day12
using System.Collections.Immutable;
using System.Diagnostics;
using AoC2021;
const string START = "start";
const string END = "end";
var paths = new Dictionary<string, ImmutableHashSet<string>>();

File.ReadAllLines("day12/input")
    .Select(l => l.Split("-"))
    .ForEachAsList(x => {
        if (x[0] != END && x[1] != START) {
            if (paths.ContainsKey(x[0])) {
                paths[x[0]] = paths[x[0]].Add(x[1]);
            } else {
                paths.Add(x[0], ImmutableHashSet.Create(x[1]));
            }
        }

        if (x[1] != END && x[0] != START) {
            if (paths.ContainsKey(x[1])) {
                paths[x[1]] = paths[x[1]].Add(x[0]);
            } else {
                paths.Add(x[1], ImmutableHashSet.Create(x[0]));
            }
        }
    });

Console.WriteLine(PathCountPart1(paths, ImmutableHashSet.Create(START), START));
Console.WriteLine(PathCountPart2(paths, ImmutableHashSet.Create(START), START, false));

long PathCountPart1(Dictionary<string, ImmutableHashSet<string>> paths, ImmutableHashSet<string> visitedSmallCaves, string current) {
    long count = paths[current].Contains(END) ? 1 : 0;
    ImmutableHashSet<string> adjacent;
    adjacent = paths[current].Except(visitedSmallCaves).Remove(END);
    foreach (var a in adjacent) {
        if (a.ToLower() == a) {
            count += PathCountPart1(paths, visitedSmallCaves.Add(a), a);
        }
        else {
            count += PathCountPart1(paths, visitedSmallCaves, a);
        }
    }

    return count;
}

long PathCountPart2(Dictionary<string, ImmutableHashSet<string>> paths, ImmutableHashSet<string> visitedSmallCaves, string current, bool twice) {
    long count = paths[current].Contains(END) ? 1 : 0;
    ImmutableHashSet<string> adjacent;
    if (twice) {
        adjacent = paths[current].Except(visitedSmallCaves).Remove(END);
    } else {
        adjacent = paths[current].Remove(END);
    }

    foreach (var a in adjacent) {
        if (a.ToLower() == a) {
            count += PathCountPart2(paths, visitedSmallCaves.Add(a), a, twice || visitedSmallCaves.Contains(a));
        }
        else {
            count += PathCountPart2(paths, visitedSmallCaves, a, twice);
        }
    }

    return count;
}

// Part Two iteratively
long count = 0;
var states = new Stack<State>();
states.Push(new State(ImmutableHashSet.Create(START), START, false));
while (states.Count > 0) {
    var s = states.Pop();
    count += paths[s.current].Contains(END) ? 1 : 0;
    ImmutableHashSet<string> adjacent;
    if (s.twice) {
        adjacent = paths[s.current].Except(s.visitedSmallCaves).Remove(END);
    } else {
        adjacent = paths[s.current].Remove(END);
    }
    foreach (var a in adjacent) {
        if (Char.IsLower(a[0])) {
            states.Push(new State(s.visitedSmallCaves.Add(a), a, s.twice || s.visitedSmallCaves.Contains(a)));
        } else {
            states.Push(new State(s.visitedSmallCaves, a, s.twice));
        }
    }
}
Console.WriteLine(count);

record State(ImmutableHashSet<string> visitedSmallCaves, string current, bool twice);
#endif