Day 3 solutions 😀

day_3/parser.ts

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+enum PARSER_STATE {
+  EMPTY,
+  NUMBER,
+}
+
+export interface Point {
+  i: number;
+  j: number;
+}
+
+export const iterPoint = (p: Point) => {
+  const adjacent_points: Point[] = [
+    { i: p.i + 1, j: p.j + 1 },
+    { i: p.i + 1, j: p.j + 0 },
+    { i: p.i + 1, j: p.j + -1 },
+    { i: p.i + 0, j: p.j + 1 },
+    // {i: p.i + 0, j: p.j + 0},
+    { i: p.i + 0, j: p.j + -1 },
+    { i: p.i + -1, j: p.j + 1 },
+    { i: p.i + -1, j: p.j + 0 },
+    { i: p.i + -1, j: p.j + -1 },
+  ];
+  return adjacent_points;
+};
+
+export interface Symbol {
+  p: Point;
+  symbol: string;
+}
+
+export const point_2_string = (p: Point) => `${p.i},${p.j}`;
+
+export const parse_file = (input: string) => {
+  const grid = input.split("\n").map((row) => row.split(""));
+
+  var parser_state = PARSER_STATE.EMPTY;
+  const part_numbers: number[] = [];
+  const part_number_cells: Map<string, number> = new Map();
+  const symbols: Symbol[] = [];
+
+  for (const j in grid) {
+    const row = grid[j];
+
+    // Numbers do not go down rows.
+    parser_state = parser_state = PARSER_STATE.EMPTY;
+    var number_buf = "";
+
+    for (const i in row) {
+      const cell = row[i];
+      const point: Point = { i: parseInt(i), j: parseInt(j) };
+      if (["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"].includes(cell)) {
+        parser_state = PARSER_STATE.NUMBER;
+        number_buf += cell;
+        part_number_cells.set(point_2_string(point), part_numbers.length);
+      } else {
+        if (parser_state === PARSER_STATE.NUMBER) {
+          part_numbers.push(parseInt(number_buf));
+          number_buf = "";
+        }
+        if (cell !== ".") {
+          symbols.push({ p: point, symbol: cell });
+        }
+        parser_state = PARSER_STATE.EMPTY;
+      }
+    }
+
+    // Cleanup at end of file.
+    if (parser_state === PARSER_STATE.NUMBER) {
+      part_numbers.push(parseInt(number_buf));
+    }
+  }
+
+  return {
+    part_numbers: part_numbers,
+    part_number_cells: part_number_cells,
+    symbols: symbols,
+  };
+};

day_3/part_1.ts

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+import * as fs from "fs";
+import { iterPoint, parse_file, point_2_string } from "./parser";
+
+const input = fs.readFileSync("input", "utf8");
+const { part_numbers, part_number_cells, symbols } = parse_file(input);
+
+const valid_part_number_indices: Set<number> = new Set();
+
+symbols.forEach((e) => {
+  iterPoint(e.p)
+    .map((e) => point_2_string(e))
+    .forEach((adjP) => {
+      const part_number_index = part_number_cells.get(adjP);
+
+      if (part_number_index !== undefined) {
+        valid_part_number_indices.add(part_number_index);
+      }
+    });
+});
+
+console.log(
+  [...valid_part_number_indices]
+    .map((i) => part_numbers[i])
+    .reduce((sum, v) => sum + v, 0)
+);

day_3/part_2.ts

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+import * as fs from "fs";
+import { iterPoint, parse_file, point_2_string } from "./parser";
+
+const input = fs.readFileSync("input", "utf8");
+const { part_numbers, part_number_cells, symbols } = parse_file(input);
+
+interface GearPair {
+  g1: number;
+  g2: number;
+}
+
+const gear_pairs: Set<GearPair> = new Set();
+
+symbols.forEach((e) => {
+  if (e.symbol === "*") {
+    const gears: Set<number> = new Set();
+    iterPoint(e.p)
+      .map((e) => point_2_string(e))
+      .forEach((adjP) => {
+        const part_number_index = part_number_cells.get(adjP);
+
+        if (part_number_index !== undefined) {
+          gears.add(part_number_index);
+        }
+      });
+    if (gears.size === 2) {
+      const gear_pair: GearPair = {
+        g1: [...gears][0],
+        g2: [...gears][1],
+      };
+      gear_pairs.add(gear_pair);
+    }
+  }
+});
+
+console.log(
+  [...gear_pairs]
+    .map((pair) => part_numbers[pair.g1] * part_numbers[pair.g2])
+    .reduce((sum, v) => sum + v, 0)
+);