Day 21 answer

Inverting the operations gave me some trouble, but I made it.

advent-of-code-2022.csproj

@@ -84,6 +84,7 @@
 	  <EmbeddedResource Include="inputs\20a.txt" />
 	  <EmbeddedResource Include="inputs\21.txt" />
 	  <None Remove="inputs\22.txt" />
+	  <EmbeddedResource Include="inputs\21a.txt" />
 	  <EmbeddedResource Include="inputs\22.txt" />
 	  <None Remove="inputs\23.txt" />
 	  <EmbeddedResource Include="inputs\23.txt" />

inputs/21a.txt

@@ -0,0 +1,15 @@
+root: pppw + sjmn
+dbpl: 5
+cczh: sllz + lgvd
+zczc: 2
+ptdq: humn - dvpt
+dvpt: 3
+lfqf: 4
+humn: 5
+ljgn: 2
+sjmn: drzm * dbpl
+sllz: 4
+pppw: cczh / lfqf
+lgvd: ljgn * ptdq
+drzm: hmdt - zczc
+hmdt: 32

src/21.cs

@@ -0,0 +1,109 @@
+namespace aoc2022;
+
+internal class Day21 : Day
+{
+    private record monkeyOp(int num, string m1, string m2, string op);
+
+    private readonly Dictionary<string, monkeyOp> monkeys = new();
+
+    internal override void Parse()
+    {
+        foreach (var line in Util.Parsing.ReadAllLines("21"))
+        {
+            var parts = line.Split(": ");
+            if (parts[1].Contains(" "))
+            {
+                var op = parts[1].Split(' ');
+                monkeys.Add(parts[0], new monkeyOp(0, op[0], op[2], op[1]));
+            }
+            else
+            {
+                monkeys.Add(parts[0], new monkeyOp(int.Parse(parts[1]), string.Empty, string.Empty, string.Empty));
+            }
+        }
+    }
+
+    private long getResultFromMonkey(string monkey)
+    {
+        var op = monkeys[monkey];
+        if (string.IsNullOrEmpty(op.m1))
+        {
+            return op.num;
+        }
+
+        var left = getResultFromMonkey(op.m1);
+        var right = getResultFromMonkey(op.m2);
+
+        return op.op switch
+        {
+            "+" => left + right,
+            "-" => left - right,
+            "*" => left * right,
+            "/" => left / right,
+            _ => throw new Exception("unhandled"),
+        };
+    }
+
+    private long getRequiredHumnResult(string monkey, long? target = null)
+    {
+        if (monkey == "humn")
+        {
+            return target!.Value;
+        }
+
+        var leftMonkey = monkeys[monkey].m1;
+        if (string.IsNullOrEmpty(leftMonkey))
+        {
+            return monkeys[monkey].num;
+        }
+
+        var rightMonkey = monkeys[monkey].m2;
+        var left1 = getResultFromMonkey(leftMonkey);
+        var right1 = getResultFromMonkey(rightMonkey);
+
+        monkeys["humn"] = new monkeyOp(monkeys["humn"].num == 0 ? 1000000 : 0, string.Empty, string.Empty, string.Empty);
+        var left2 = getResultFromMonkey(leftMonkey);
+
+        long result;
+        if (left1 != left2)
+        {
+            target = monkeys[monkey].op switch
+            {
+                "+" => target - right1,
+                "-" => target + right1,
+                "*" => target / right1,
+                "/" => target * right1,
+                _ => throw new Exception("unhandled"),
+            };
+            result = getRequiredHumnResult(leftMonkey, target ?? right1);
+        }
+        else
+        {
+            target = monkeys[monkey].op switch
+            {
+                "+" => target - left1,
+                "-" => left1 - target,
+                "*" => target / left1,
+                "/" => left1 / target,
+                _ => throw new Exception("unhandled"),
+            };
+            result = getRequiredHumnResult(rightMonkey, target ?? left1);
+        }
+
+        return result;
+    }
+
+    internal override string Part1()
+    {
+        var result = getResultFromMonkey("root");
+
+        return $"<+white>{result}";
+    }
+
+    internal override string Part2()
+    {
+        var result = getRequiredHumnResult("root");
+
+        return $"<+white>{result}";
+    }
+}