Day Fifteen

index.ts

@@ -1,3 +1,3 @@
-import {runDayTen} from "./src/day_ten";
+import {runDayFifteen} from "./src/day_fifteen";
 
-runDayTen();
+runDayFifteen();

src/day_fifteen.test.ts

@@ -0,0 +1,30 @@
+import {totalFocusingPower, hash, hashSum} from "./day_fifteen";
+
+describe('Day Fifteen', () => {
+   it.each([
+       ['HASH', 52],
+       ['rn=1', 30],
+       ['cm-', 253],
+       ['qp=3', 97],
+       ['cm=2', 47],
+       ['qp-', 14],
+       ['pc=4', 180],
+       ['ot=9', 9],
+       ['ab=5', 197],
+       ['pc-', 48],
+       ['pc=6', 214],
+       ['ot=7', 231],
+   ])('calculates the hash of %s to %s', (input, expected) => {
+         expect(hash(input)).toBe(expected);
+   });
+
+   it('calculates the hash of the example', () => {
+      const input = 'rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7';
+      expect(hashSum(input)).toEqual(1320);
+   });
+
+   it('calculates the focusing power', () => {
+       const input = 'rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7';
+       expect(totalFocusingPower(input)).toEqual(145);
+   })
+});

src/day_fifteen.ts

@@ -0,0 +1,57 @@
+import fs from "fs";
+
+export const hash = (input: string): number => {
+    const parts = input.split('');
+    let hash = 0;
+    for (let i = 0; i < parts.length; i++) {
+        hash += parts[i].charCodeAt(0);
+        hash *= 17;
+        hash %= 256;
+    }
+    return hash;
+}
+
+export const hashSum = (input: string): number => {
+    return input.split(',').reduce((sum, part) => sum + hash(part), 0);
+}
+
+
+const focusingPower = (boxNumber: number, slot: number, value: number): number => {
+    return (1 + boxNumber) * (1 + slot) * value;
+}
+
+export const totalFocusingPower = (input: string): number => {
+    const boxes: [string, number][][] = new Array(256).fill(0).map(() => []);
+
+    input.split(',').forEach(part => {
+        if (part.includes('=')) {
+            const [label, value] = part.split('=');
+            const box = hash(label);
+            const index = boxes[box].findIndex(([l]) => l === label);
+            boxes[hash(label)].splice(index === -1 ? boxes[box].length : index, 1, [label, parseInt(value)]);
+        } else {
+            const [label] = part.split('-');
+            let box = hash(label);
+            const index = boxes[box].findIndex(([l]) => l === label);
+            if (index !== -1) {
+                boxes[box].splice(index, 1);
+            }
+        }
+    });
+
+    return boxes.reduce(
+        (sum, box, boxIndex) =>
+            sum + box.reduce(
+                (total, [label, value], slot) => {
+                    return total + focusingPower(boxIndex, slot, value)
+                },
+                0
+            ),
+        0
+    );
+}
+
+export const runDayFifteen = () => {
+    const input = fs.readFileSync('./inputs/day_fifteen_input.txt', 'utf-8').trimEnd();
+    console.log('Day Fifteen output:', totalFocusingPower(input));
+}