diff --git a/2024/12/2024-12.run.xml b/2024/12/2024-12.run.xml
new file mode 100644
index 0000000..178a12d
--- /dev/null
+++ b/2024/12/2024-12.run.xml
@@ -0,0 +1,7 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="2024-12" type="BunRunConfiguration">
+    <option name="program" value="2024/12/run.ts" />
+    <option name="workingDirectory" value="$PROJECT_DIR$" />
+    <method v="2" />
+  </configuration>
+</component>
\ No newline at end of file
diff --git a/2024/12/index.test.ts b/2024/12/index.test.ts
new file mode 100644
index 0000000..90746d8
--- /dev/null
+++ b/2024/12/index.test.ts
@@ -0,0 +1,78 @@
+import { describe, expect, it } from 'bun:test';
+import { getSides, solveFirst, solveSecond } from './index.ts';
+
+describe('2024-12', () => {
+  it('first', () => {
+    expect(
+      solveFirst(`AAAA
+BBCD
+BBCC
+EEEC`)
+    ).toBe(140);
+    expect(
+      solveFirst(`OOOOO
+OXOXO
+OOOOO
+OXOXO
+OOOOO`)
+    ).toBe(772);
+    expect(
+      solveFirst(`RRRRIICCFF
+RRRRIICCCF
+VVRRRCCFFF
+VVRCCCJFFF
+VVVVCJJCFE
+VVIVCCJJEE
+VVIIICJJEE
+MIIIIIJJEE
+MIIISIJEEE
+MMMISSJEEE`)
+    ).toBe(1930);
+  });
+
+  it('second', () => {
+    // it takes too long
+    // so only run while `NODE_ENV=production bun test --coverage`
+    if (process.env.NODE_ENV === 'production') {
+      expect(
+        solveSecond(`EEEEE
+EXXXX
+EEEEE
+EXXXX
+EEEEE`)
+      ).toBe(236);
+      expect(
+        solveSecond(`AAAA
+BBCD
+BBCC
+EEEC`)
+      ).toBe(80);
+      expect(
+        solveSecond(`OOOOO
+OXOXO
+OOOOO
+OXOXO
+OOOOO`)
+      ).toBe(436);
+      expect(
+        solveSecond(`AAAAAA
+AAABBA
+AAABBA
+ABBAAA
+ABBAAA
+AAAAAA`)
+      ).toBe(368);
+    }
+  });
+
+  it('sides', () => {
+    expect(
+      getSides([
+        [0, 0],
+        [1, 0],
+        [2, 0],
+        [0, 1]
+      ])
+    ).toBe(6);
+  });
+});
diff --git a/2024/12/index.ts b/2024/12/index.ts
new file mode 100644
index 0000000..f7b0847
--- /dev/null
+++ b/2024/12/index.ts
@@ -0,0 +1,113 @@
+import { sumArray } from '../../utils/array.ts';
+import {
+  calculateSides,
+  type Coordinates,
+  getAdjacent,
+  getNeighbouringSides,
+  isCoordinateEqual
+} from '../../utils/coordinates.ts';
+
+function searchNeighbours(
+  visited: Set<number>,
+  rows: string[],
+  char: string,
+  x: number,
+  y: number,
+  found: Coordinates
+) {
+  const position = y * rows.length + x;
+  if (visited.has(position)) {
+    return;
+  }
+  visited.add(position);
+  found.push([x, y]);
+
+  const { left, top, right, down } = getAdjacent(rows, x, y);
+  if (left === char) {
+    searchNeighbours(visited, rows, char, x - 1, y, found);
+  }
+  if (top === char) {
+    searchNeighbours(visited, rows, char, x, y - 1, found);
+  }
+  if (right === char) {
+    searchNeighbours(visited, rows, char, x + 1, y, found);
+  }
+  if (down === char) {
+    searchNeighbours(visited, rows, char, x, y + 1, found);
+  }
+}
+
+function groupChars(input: string) {
+  const rows = input.split('\n');
+
+  const groups: { char: string; coords: Coordinates }[] = [];
+  const visited = new Set<number>();
+
+  for (let y = 0; y < rows.length; y++) {
+    for (let x = 0; x < rows[y].length; x++) {
+      const position = y * rows.length + x;
+      if (visited.has(position)) {
+        continue;
+      }
+      const char = rows[y][x];
+      const coords: Coordinates = [];
+      searchNeighbours(visited, rows, char, x, y, coords);
+
+      groups.push({ char, coords });
+    }
+  }
+  return groups;
+}
+
+function getPerimeter(g: Coordinates): number {
+  if (g.length === 1) {
+    return 4;
+  }
+  if (g.length === 2) {
+    return 6;
+  }
+  const { uniqueSides } = calculateSides(g);
+
+  return uniqueSides.length;
+}
+
+export function solveFirst(input: string): number {
+  const groups = groupChars(input);
+
+  return sumArray(groups.map((g) => g.coords.length * getPerimeter(g.coords)));
+}
+
+export function solveSecond(input: string): number {
+  const groups = groupChars(input);
+
+  return sumArray(groups.map((g) => g.coords.length * getSides(g.coords)));
+}
+
+export function getSides(g: Coordinates): number {
+  if (g.length === 1) {
+    return 4;
+  }
+  if (g.length === 2) {
+    return 4;
+  }
+  const { uniqueSides } = calculateSides(g);
+
+  const visited = new Set<number>();
+
+  let sides = 0;
+  for (let i = 0; i < uniqueSides.length; i++) {
+    if (visited.has(i)) {
+      continue;
+    }
+    visited.add(i);
+    sides++;
+
+    const { neighbours } = getNeighbouringSides(uniqueSides[i], uniqueSides);
+
+    neighbours.forEach((c) =>
+      visited.add(uniqueSides.findIndex((v) => isCoordinateEqual(v, c)))
+    );
+  }
+
+  return sides;
+}
diff --git a/2024/12/run.ts b/2024/12/run.ts
new file mode 100644
index 0000000..88783cd
--- /dev/null
+++ b/2024/12/run.ts
@@ -0,0 +1,12 @@
+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);
diff --git a/utils/coordinates.ts b/utils/coordinates.ts
index c13cb95..5c79c57 100644
--- a/utils/coordinates.ts
+++ b/utils/coordinates.ts
@@ -1,5 +1,16 @@
+export const Sides = {
+  TOP: 0,
+  RIGHT: 1,
+  DOWN: 2,
+  LEFT: 3
+} as const;
+
+export type Side = (typeof Sides)[keyof typeof Sides];
+
 export type Coordinate = [number, number];
+export type CoordinateSide = [number, number, Side];
 export type Coordinates = Coordinate[];
+export type CoordinateSides = CoordinateSide[];
 
 /**
  * Returns a filter lambda to be used in array.filter() on a xy-Coordinate array (array of two number arrays).
@@ -9,7 +20,7 @@ export type Coordinates = Coordinate[];
  * @param yMin Inclusive, defaults to 0
  */
 export function inBounds(xMax: number, yMax: number, xMin = 0, yMin = 0) {
-  return ([x, y]: Readonly<Coordinate>) =>
+  return ([x, y]: Readonly<Coordinate | CoordinateSide>) =>
     x >= xMin && x < xMax && y >= yMin && y < yMax;
 }
 
@@ -19,8 +30,8 @@ export function inBounds(xMax: number, yMax: number, xMin = 0, yMin = 0) {
  * @param b xy-Coordinate, two number array
  */
 export function isCoordinateEqual(
-  a: Readonly<Coordinate>,
-  b: Readonly<Coordinate>
+  a: Readonly<Coordinate | CoordinateSide>,
+  b: Readonly<Coordinate | CoordinateSide>
 ): boolean {
   return b[0] === a[0] && b[1] === a[1];
 }
@@ -78,3 +89,45 @@ export function findCoordsOfDigit(
     []
   );
 }
+
+export function calculateSides(g: Coordinate[]) {
+  const allSides = g.flatMap(
+    ([x, y]) =>
+      [
+        [x - 0.5, y, Sides.LEFT],
+        [x, y - 0.5, Sides.TOP],
+        [x + 0.5, y, Sides.RIGHT],
+        [x, y + 0.5, Sides.DOWN]
+      ] as CoordinateSides
+  );
+
+  const uniqueSides = allSides.filter(
+    (c) => allSides.filter((b) => isCoordinateEqual(c, b)).length === 1
+  );
+  return { uniqueSides, allSides };
+}
+
+export function getNeighbouringSides(
+  from: CoordinateSide,
+  all: CoordinateSides
+) {
+  const [x, y, side] = from;
+  const isVertical = Math.abs(x % 1) === 0.5;
+  const coordIndex = isVertical ? 1 : 0;
+
+  const allDirectional = all
+    .filter(([cx, cy, cs]) => (isVertical ? cx === x : cy === y) && cs === side)
+    .toSorted((a, b) => a[coordIndex] - b[coordIndex]);
+
+  const before = allDirectional
+    .filter((d) => d[coordIndex] - from[coordIndex] < 0)
+    .toSorted((a, b) => b[coordIndex] - a[coordIndex])
+    .filter((d, i) => d[coordIndex] - from[coordIndex] === 0 - i - 1);
+  const after = allDirectional
+    .filter((d) => d[coordIndex] - from[coordIndex] > 0)
+    .filter((d, i) => d[coordIndex] - from[coordIndex] === i + 1);
+
+  const neighbours = [...before, ...after];
+
+  return { before, after, neighbours };
+}