Add gear ratio calculation function and tests

Author: vicainelli

src/day-03/example.txt

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+467..114............23
+...*......
+..35..633.
+......#...
+617*......
+.....+.58.
+..592.....
+......755.
+...$.*....
+.664.598..

src/day-03/gear-ratios.test.ts

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+import { describe, expect, test } from "bun:test";
+import { gearRatioPartOne } from "./gear-ratios";
+
+const example = Bun.file("src/day-03/example.txt");
+const content_example = await example.text();
+
+const input = Bun.file("src/day-03/input.txt");
+const content_input = await input.text();
+
+describe("Day 03, gear ratios", () => {
+  describe("Part One", () => {
+    test("it should return 4361, example", () => {
+      const result = gearRatioPartOne(content_example);
+      expect(result).toEqual(4361);
+    });
+
+    test("it should return 525119, input", () => {
+      const result = gearRatioPartOne(content_input);
+      expect(result).toEqual(525119);
+    });
+  });
+});

src/day-03/gear-ratios.ts

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+const isSymbol = (str: string): boolean => {
+  return str !== "."; // numbers touching numbers is not the case, so handling only `.`
+};
+
+const isNumber = (str: string): boolean => {
+  return !Number.isNaN(parseInt(str));
+};
+
+const isGear = (str: string): boolean => {
+  return str === "*";
+};
+export function gearRatioPartOne(content: string): number {
+  const lines = content.trim().split("\n");
+
+  const matrix = lines.map((line) => line.split(""));
+
+  let total = 0;
+
+  for (let lineIdx = 0; lineIdx < lines.length; lineIdx++) {
+    let match;
+    const pattern = /\d+/g;
+
+    while ((match = pattern.exec(lines[lineIdx])) !== null) {
+      const arround: boolean[] = [];
+
+      // * Left
+      // check if `lineIdx` or `match.index - 1` is negative
+      if (
+        lineIdx >= 0 &&
+        match.index - 1 >= 0 &&
+        matrix[lineIdx] &&
+        matrix[lineIdx][match.index - 1]
+      ) {
+        const matrixLeft = matrix[lineIdx][match.index - 1];
+        arround.push(isSymbol(matrixLeft)); // * left side
+      }
+
+      // * Right
+      if (
+        lineIdx >= 0 &&
+        pattern.lastIndex >= 0 &&
+        matrix[lineIdx] &&
+        matrix[lineIdx][pattern.lastIndex]
+      ) {
+        const matrixRight = matrix[lineIdx][pattern.lastIndex];
+        arround.push(isSymbol(matrixRight)); // * right side
+      }
+
+      for (let i = match.index - 1; i <= pattern.lastIndex; i++) {
+        // * TOP ====================
+        // * Check if:
+        // * - lineIdx - 1 is NOT negative
+        // * - i is NOT negative
+        // * - matrix[lineIdx - 1] is valid
+        // * - matrix[lineIdx - 1][i] is valid
+        if (
+          lineIdx - 1 >= 0 &&
+          i >= 0 &&
+          matrix[lineIdx - 1] &&
+          matrix[lineIdx - 1][i]
+        ) {
+          const matrixTop = matrix[lineIdx - 1][i];
+          arround.push(isSymbol(matrixTop));
+        }
+
+        // * BOTTOM ====================
+        // check if lineIdx + 1 or i is negative, and is not bigger than the matrix length
+        if (
+          lineIdx + 1 >= 0 &&
+          i >= 0 &&
+          matrix[lineIdx + 1] &&
+          matrix[lineIdx + 1][i]
+        ) {
+          const matrixBottom = matrix[lineIdx + 1][i];
+          arround.push(isSymbol(matrixBottom));
+        }
+      }
+
+      if (arround.includes(true)) {
+        total += Number(match[0]);
+      }
+    }
+  }
+
+  return total;
+}