day 7 done

day7/mod.ts

@@ -1,17 +1,60 @@
 export function parse(data_r: string): [number, number[]][] {
   const data = data_r.trim();
   return data.split("\n").map((line) => {
-    const ecase = line.split(":");
-    return [Number(ecase[0]), ecase[1].split(",").map(Number)];
+    const [a, b] = line.split(":");
+    return [Number(a.trim()), b.trim().split(" ").map(Number)];
   });
 }
 
+function solve1_util(value: number, remaining: number[]): boolean {
+  if (remaining.length === 1) {
+    return remaining[0] === value;
+  }
+  const [head, ...tail] = remaining;
+  // input is reversed
+  //   tail + head = value
+  //   tail * head = value
+  return (head <= value && solve1_util(value - head, tail)) ||
+    (value % head == 0 && solve1_util(value / head, tail));
+}
+
+function solve2_util(value: number, remaining: number[]): boolean {
+  if (remaining.length === 1) {
+    return remaining[0] === value;
+  }
+  const [head, ...tail] = remaining;
+  // input is reversed
+  //   tail + head = value
+  //   tail * head = value
+  //   tail | head = value
+  const value_str = value.toString();
+  const head_str = head.toString();
+  if (value_str.length > head_str.length && value_str.endsWith(head_str)) {
+    const new_value_str = value_str.slice(
+      0,
+      value_str.length - head_str.length,
+    );
+    const new_value = Number(new_value_str);
+    if (solve2_util(new_value, tail)) {
+      return true;
+    }
+  }
+  return (head <= value && solve2_util(value - head, tail)) ||
+    (value % head == 0 && solve2_util(value / head, tail));
+}
+
 export function solve1(data: [number, number[]][]): number {
-  return data.length;
+  return data.filter((ecase) => {
+    // reverse will reverse the array in place too
+    return solve1_util(ecase[0], ecase[1].slice().reverse());
+  }).reduce((acc, [value, _]) => acc + value, 0);
 }
 
 export function solve2(data: [number, number[]][]): number {
-  return data.length;
+  return data.filter((ecase) => {
+    // reverse will reverse the array in place too
+    return solve2_util(ecase[0], ecase[1].slice().reverse());
+  }).reduce((acc, [value, _]) => acc + value, 0);
 }
 
 if (import.meta.main) {

day7/test.ts

@@ -4,6 +4,6 @@ import { parse, solve1, solve2 } from "./mod.ts";
 Deno.test(async function testExample() {
   const example_data_path = new URL("example.txt", import.meta.url).pathname;
   const example_data = parse(await Deno.readTextFile(example_data_path));
-  assertEquals(solve1(example_data), 9);
-  assertEquals(solve2(example_data), 9);
+  assertEquals(solve1(example_data), 3749);
+  assertEquals(solve2(example_data), 11387);
 });