Solve 2025-09

2025/09/2025-09.run.xml

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+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="2025-09" type="BunRunConfiguration">
+    <option name="program" value="2025/09/run.ts" />
+    <option name="workingDirectory" value="$PROJECT_DIR$" />
+    <method v="2" />
+  </configuration>
+</component>

2025/09/index.test.ts

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+import { describe, expect, it } from 'bun:test';
+import { solveFirst, solveSecond } from './index.ts';
+
+describe('2025-09', () => {
+  const testInput = `7,1
+11,1
+11,7
+9,7
+9,5
+2,5
+2,3
+7,3`;
+  it('first', () => {
+    expect(solveFirst(testInput)).toBe(50);
+  });
+  it('second', () => {
+    expect(solveSecond(testInput)).toBe(25);
+  });
+});

2025/09/index.ts

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+import { uniqueCombinations } from '../../utils/array.ts';
+import type { Coordinate } from '../../utils/coordinates.ts';
+
+export function solveFirst(input: string): number {
+  const reds = input
+    .split('\n')
+    .map((r) => r.split(',').map(Number) as Coordinate);
+
+  const combs = uniqueCombinations(reds)
+    .map(
+      ({ a, b }) => (Math.abs(a[0] - b[0]) + 1) * (Math.abs(a[1] - b[1]) + 1)
+    )
+    .toSorted((a, b) => b - a);
+  return combs[0];
+}
+
+function calcArea(a: Coordinate, b: Coordinate) {
+  return (Math.abs(a[0] - b[0]) + 1) * (Math.abs(a[1] - b[1]) + 1);
+}
+
+export function solveSecond(input: string): number {
+  const reds = input
+    .split('\n')
+    .map((r) => r.split(',').map(Number) as Coordinate);
+
+  const lines: Line[] = [];
+  for (let i = 1; i < reds.length; i++) {
+    lines.push([reds[i - 1], reds[i]]);
+  }
+  lines.push([reds[reds.length - 1], reds[0]]);
+
+  let maxArea = 0;
+
+  for (let i = 0; i < reds.length; i++) {
+    for (let j = i + 1; j < reds.length; j++) {
+      if (reds[i][0] == reds[j][0] || reds[i][1] == reds[j][1]) continue;
+      const rectLines: Line[] = [
+        [reds[i], reds[j]],
+        [
+          [reds[i][0], reds[j][1]],
+          [reds[j][0], reds[i][1]]
+        ]
+      ];
+
+      if (
+        rectLines.some((rline) => lines.some((line) => intersects(rline, line)))
+      ) {
+        continue;
+      }
+
+      maxArea = Math.max(maxArea, calcArea(reds[i], reds[j]));
+    }
+  }
+
+  return maxArea;
+}
+
+/**
+ * Checks for intersection of two lines.
+ * @param abcd Line (a,b)->(c,d)
+ * @param pqrs Line (p,q)->(r,s)
+ *
+ * @see {@link https://stackoverflow.com/a/24392281/11271734|Source}
+ */
+export function intersects(abcd: Line, pqrs: Line) {
+  const [a, b, c, d] = abcd.flat();
+  const [p, q, r, s] = pqrs.flat();
+  const det = (c - a) * (s - q) - (r - p) * (d - b);
+  if (det === 0) {
+    return false;
+  } else {
+    const lambda = ((s - q) * (r - a) + (p - r) * (s - b)) / det;
+    const gamma = ((b - d) * (r - a) + (c - a) * (s - b)) / det;
+    return 0 < lambda && lambda < 1 && 0 < gamma && gamma < 1;
+  }
+}
+
+type Line = [Coordinate, Coordinate];

2025/09/run.ts

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+import { join } from 'path';
+import { solveFirst, solveSecond } from './index.ts';
+
+const input = await Bun.file(join(__dirname, 'input.txt')).text();
+
+const firstAnswer = solveFirst(input);
+
+console.log(firstAnswer);
+
+const secondAnswer = solveSecond(input);
+
+console.log(secondAnswer);