Solve 2024-19

2024/19/index.ts

@@ -0,0 +1,79 @@
+import { sumArray } from '../../utils/array.ts';
+
+export function solveFirst(input: string): number {
+  const [row, lines] = input.split('\n\n');
+  const towels = row.split(', ').toSorted((a, b) => b.length - a.length);
+  const combinations = lines.split('\n');
+
+  const possibleCombinations = combinations.filter((c) =>
+    isPossible(c, towels)
+  );
+  return possibleCombinations.length;
+}
+
+const lookup = new Map<string, number>();
+
+export function allPossibilities(
+  combination: string,
+  towels: string[]
+): number {
+  const lookedUp = lookup.get(combination);
+  if (lookedUp !== undefined) {
+    return lookedUp;
+  }
+  if (combination.length <= 0) {
+    lookup.set(combination, 1);
+    return 1;
+  }
+  const prefixes = towels.filter((t) => combination.startsWith(t));
+  if (prefixes.length <= 0) {
+    lookup.set(combination, 0);
+    return 0;
+  }
+
+  const result = sumArray(
+    prefixes.map((p) =>
+      allPossibilities(combination.substring(p.length), towels)
+    )
+  );
+  lookup.set(combination, result);
+
+  return result;
+}
+
+const lookupPossible = new Map<string, boolean>();
+
+export function isPossible(combination: string, towels: string[]): boolean {
+  const lookedUp = lookupPossible.get(combination);
+  if (lookedUp !== undefined) {
+    return lookedUp;
+  }
+  if (combination.length <= 0) {
+    lookupPossible.set(combination, true);
+    return true;
+  }
+  const prefixes = towels.filter((t) => combination.startsWith(t));
+  if (prefixes.length <= 0) {
+    lookupPossible.set(combination, false);
+    return false;
+  }
+
+  const result = prefixes.some((p) =>
+    isPossible(combination.substring(p.length), towels)
+  );
+  lookupPossible.set(combination, result);
+
+  return result;
+}
+
+export function solveSecond(input: string): number {
+  const [row, lines] = input.split('\n\n');
+  const towels = row.split(', ').toSorted((a, b) => b.length - a.length);
+  const combinations = lines.split('\n');
+
+  const possibleCombinations = combinations.map((c) =>
+    allPossibilities(c, towels)
+  );
+
+  return sumArray(possibleCombinations);
+}