Day 21

21/solution.mjs

@@ -0,0 +1,139 @@
+import { readFileSync } from 'node:fs';
+
+const input = readFileSync('input', 'utf-8');
+
+class Monkey {
+  constructor(monkeys, name) {
+    this.monkeys = monkeys;
+    this.name = name;
+    this.value = undefined;
+    this.formulas = [];
+    this.aliases = [];
+  }
+
+  addFormula(left, operator, right) {
+    this.formulas.push([left, operator, right]);
+    return this;
+  }
+
+  removeFormulasInvolving(name) {
+    this.formulas = this.formulas.filter(
+      ([left, _, right]) => left !== name && right !== name
+    );
+    return this;
+  }
+
+  addAlias(name) {
+    this.aliases.push(name);
+    return this;
+  }
+  
+  setValue(value) {
+    this.value = value;
+    return this;
+  }
+
+  solve(path = []) {
+    if (this.value !== undefined) {
+      return this.value;
+    }
+    for (const name of this.aliases) {
+      if (path.includes(name)) {
+        continue;
+      }
+      const value = this.monkeys[name].solve([...path, this.name]);
+      if (value !== 'UNKNOWN') {
+        return value;
+      }
+    }
+    for (const [left, operator, right] of this.formulas) {
+      if (path.includes(left) || path.includes(right)) {
+        continue;
+      }
+
+      const leftValue = this.monkeys[left].solve([...path, this.name]);
+      const rightValue = this.monkeys[right].solve([...path, this.name]);
+
+      if (leftValue === 'UNKNOWN' || rightValue === 'UNKNOWN') {
+        continue;
+      }
+
+      switch (operator) {
+        case '*': return leftValue * rightValue;
+        case '/': return leftValue / rightValue;
+        case '+': return leftValue + rightValue;
+        case '-': return leftValue - rightValue;
+      }
+    }
+    return 'UNKNOWN';
+  }
+}
+
+const monkeys = {};
+function getMonkey(name) {
+  if (!monkeys.hasOwnProperty(name)) {
+    monkeys[name] = new Monkey(monkeys, name)
+  }
+  return monkeys[name];
+}
+
+input
+  .split('\n')
+  .filter(line => !!line.trim())
+  .forEach(line => {
+    const match = line.match(/^(\w+):\s+(.+?)\s*$/);
+    if (!match) {
+      throw new Error(`Invalid monkey: ${line}`);
+    }
+    const name = match[1];
+    const job = match[2];
+
+    if (/^\d+$/.test(job)) {
+      getMonkey(name).setValue(parseInt(job));
+    } else {
+      const match = job.match(/^(\w+)\s*([*\/+\-=])\s*(\w+)$/);
+      if (!match) {
+        throw new Error(`Invalid formula: ${formula}`);
+      }
+      const left = match[1];
+      const operator = match[2];
+      const right = match[3];
+
+      switch (operator) {
+        case '*':
+          getMonkey(name).addFormula(left, '*', right);
+          getMonkey(left).addFormula(name, '/', right);
+          getMonkey(right).addFormula(name, '/', left);
+          break;
+        case '/':
+          getMonkey(name).addFormula(left, '/', right);
+          getMonkey(left).addFormula(name, '*', right);
+          getMonkey(right).addFormula(left, '/', name);
+          break;
+        case '-':
+          getMonkey(name).addFormula(left, '-', right);
+          getMonkey(left).addFormula(name, '+', right);
+          getMonkey(right).addFormula(left, '-', name);
+          break;
+        case '+':
+          getMonkey(name).addFormula(left, '+', right);
+          getMonkey(left).addFormula(name, '-', right);
+          getMonkey(right).addFormula(name, '-', left);
+          break;
+        default:
+          throw new Error(`Invalid operator: ${operator}`);
+      }
+    }
+  });
+
+const rootYells = monkeys['root'].solve();
+console.log('The root monkey will yell:', rootYells);
+
+for (const monkey of Object.values(monkeys)) {
+  monkey.removeFormulasInvolving('root');
+}
+const {0: left, 2: right} = monkeys['root'].formulas[0];
+monkeys[left].addAlias(right);
+monkeys[right].addAlias(left);
+const humnYells = monkeys['humn'].setValue(undefined).solve();
+console.log('To pass roots equality test, yell:', humnYells);