feat: day 7 (#9)

* day 7 init

* day 7 done

day7/deno.json

@@ -0,0 +1,7 @@
+{
+  "name": "@scope/day7",
+  "version": "0.1.0",
+  "exports": {
+    ".": "./mod.ts"
+  }
+}

day7/example.txt

@@ -0,0 +1,9 @@
+190: 10 19
+3267: 81 40 27
+83: 17 5
+156: 15 6
+7290: 6 8 6 15
+161011: 16 10 13
+192: 17 8 14
+21037: 9 7 18 13
+292: 11 6 16 20

day7/mod.ts

@@ -0,0 +1,65 @@
+export function parse(data_r: string): [number, number[]][] {
+  const data = data_r.trim();
+  return data.split("\n").map((line) => {
+    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.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.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) {
+  const data_path = new URL("input.txt", import.meta.url).pathname;
+  const data = parse(await Deno.readTextFile(data_path));
+  console.log(solve1(data));
+  console.log(solve2(data));
+}

day7/test.ts

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+import { assertEquals } from "@std/assert";
+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), 3749);
+  assertEquals(solve2(example_data), 11387);
+});