feat(day03): Part 1

Author: coderbyheart

day03_test.ts

@@ -0,0 +1,136 @@
+import { assertEquals } from "https://deno.land/std@0.208.0/assert/assert_equals.ts";
+import { sum } from "./util/sum.ts";
+
+/**
+ * Here is an example engine schematic:
+ */
+const schematics = [
+  `467..114..`,
+  `...*......`,
+  `..35..633.`,
+  `......#...`,
+  `617*......`,
+  `.....+.58.`,
+  `..592.....`,
+  `......755.`,
+  `...$.*....`,
+  `.664.598.1`,
+];
+
+Deno.test("Day 3: Gear Ratios", async (t) => {
+  await t.step("Example", async (t) => {
+    await t.step(
+      "findPartNumbers()",
+      () =>
+        assertEquals(findPartNumbers(schematics), [
+          { n: 467, s: ["*"] },
+          { n: 114, s: [] },
+          { n: 35, s: ["*"] },
+          { n: 633, s: ["#"] },
+          { n: 617, s: ["*"] },
+          { n: 58, s: [] },
+          { n: 592, s: ["+"] },
+          { n: 755, s: ["*"] },
+          { n: 664, s: ["$"] },
+          { n: 598, s: ["*"] },
+          { n: 1, s: [] },
+        ]),
+    );
+
+    await t.step(`Calculate the example solution`, () =>
+      assertEquals(
+        sum(
+          findPartNumbers(schematics)
+            .filter(({ s }) => s.length > 0)
+            .map(({ n }) => n),
+        ),
+        4361,
+      ));
+  });
+
+  await t.step("Solution", async () => {
+    const numbers = findPartNumbers(
+      (await Deno.readTextFile("./input/day03.txt")).split("\n"),
+    );
+    assertEquals(
+      sum(
+        numbers.filter(({ s }) => s.length > 0)
+          .map(({ n }) => n),
+      ),
+      529618,
+    );
+  });
+});
+
+/**
+ * Find the part numbers in the schematics and the adjacent symbol(s)
+ */
+const findPartNumbers = (
+  schematics: string[],
+): { n: number; s: string[] }[] => {
+  const numbers: { n: number; s: string[] }[] = [];
+  let currentNumber: string[] = [];
+  let adjacentSymbols: string[] = [];
+
+  // Add parsed number with symbols to stash
+  const addNumber = () => {
+    if (currentNumber.length > 0) {
+      numbers.push({
+        n: parseInt(currentNumber.join("")),
+        s: [...new Set(adjacentSymbols)],
+      });
+    }
+    currentNumber = [];
+    adjacentSymbols = [];
+  };
+
+  for (let row = 0; row < schematics.length; row++) {
+    for (let col = 0; col < schematics[row].length; col++) {
+      const c = schematics[row][col];
+      if (/\d/.test(c)) { // Current symbol is a number
+        currentNumber.push(c);
+        const s = findAdjacentSymbols(schematics, row, col);
+        if (s !== undefined) adjacentSymbols.push(...s);
+      } else {
+        addNumber();
+      }
+    }
+  }
+  addNumber();
+  return numbers;
+};
+
+/**
+ * Find adjacent symbols for a given field
+ */
+const findAdjacentSymbols = (
+  schematics: string[],
+  row: number,
+  col: number,
+): string[] =>
+  [
+    findSymbolAt(schematics, row, col - 1), // left
+    findSymbolAt(schematics, row - 1, col - 1), // top left
+    findSymbolAt(schematics, row - 1, col), // top
+    findSymbolAt(schematics, row - 1, col + 1), // top right
+    findSymbolAt(schematics, row, col + 1), // right
+    findSymbolAt(schematics, row + 1, col + 1), // bottom right
+    findSymbolAt(schematics, row + 1, col), // bottom
+    findSymbolAt(schematics, row + 1, col - 1), // bottom left
+  ].filter((s) => s !== undefined) as string[];
+
+/**
+ * Return the symbol at a given position
+ */
+const findSymbolAt = (
+  schematics: string[],
+  row: number,
+  col: number,
+): string | undefined => {
+  if (col < 0) return undefined; // Outside of schematics
+  if (row < 0) return undefined; // Outside of schematics
+  const c = schematics[row]?.[col];
+  if (/\d/.test(c)) return undefined; // a number
+  if (c === ".") return undefined; // a dot, ignore
+  return c;
+};