AoC2025: day 6 part 2

Author: martapanc

2024-2025/src/2025/day06/day06.test.ts

@@ -7,7 +7,7 @@ describe('2025 Day 6', () => {
     });
 
     test('Part 2', async () => {
-        // expect(await part2('testInput1')).toEqual(31);
-        // expect(await part2('input')).toEqual(29379307);
+        expect(await part2('testInput1')).toEqual(3263827);
+        expect(await part2('input')).toEqual(11159825706149);
     });
 });

2024-2025/src/2025/day06/day06.ts

@@ -1,13 +1,17 @@
 import path from "node:path";
 import {readInputLineByLine} from "@utils/io";
-import {forEach} from "mathjs";
-
 export async function part1(inputFile: string) {
     return await day6(inputFile, calcGrantTotal);
 }
 
 export async function part2(inputFile: string) {
-    return await day6(inputFile);
+    return await day6raw(inputFile, calcGrantTotalCephalopod);
+}
+
+async function day6raw(inputFile: string, calcFn: (lines: string[]) => number) {
+    const inputPath = path.join(__dirname, inputFile);
+    const lines = await readInputLineByLine(inputPath);
+    return calcFn(lines);
 }
 
 async function day6(inputFile: string, calcFn?: (numberRows: number[][], ops: string[]) => number) {
@@ -20,6 +24,46 @@ async function day6(inputFile: string, calcFn?: (numberRows: number[][], ops: st
     return calcFn?.(numberRows, ops);
 }
 
+function calcGrantTotalCephalopod(lines: string[]): number {
+    const maxLen = Math.max(...lines.map(l => l.length));
+    const grid = lines.map(line => line.padEnd(maxLen, ' '));
+    const numRows = grid.length - 1; // exclude operator row
+    const opRow = grid[grid.length - 1];
+
+    // Problems are separated by full blank columns across all rows.
+    const separatorCols: boolean[] = Array.from({ length: maxLen }, (_, c) =>
+        grid.every(row => row[c] === ' ')
+    );
+
+    const spans: Array<[number, number]> = [];
+    let start = 0;
+    for (let c = 0; c <= maxLen; c++) {
+        if (c === maxLen || separatorCols[c]) {
+            if (start <= c - 1) spans.push([start, c - 1]);
+            start = c + 1;
+        }
+    }
+
+    let total = 0;
+    for (let p = spans.length - 1; p >= 0; p--) {
+        const [startCol, endCol] = spans[p];
+        const op = opRow.slice(startCol, endCol + 1).split('').find(ch => ch !== ' ');
+        if (!op) continue;
+        const numbers: number[] = [];
+
+        // Read columns right-to-left within this problem's range
+        for (let c = endCol; c >= startCol; c--) {
+            const chars = Array.from({ length: numRows }, (_, r) => grid[r][c]);
+            if (chars.every(ch => ch === ' ')) continue;
+            const digits = chars.filter(ch => ch !== ' ').join('');
+            numbers.push(Number(digits));
+        }
+
+        total += numbers.reduce((acc, cur) => op === '+' ? acc + cur : acc * cur, op === '+' ? 0 : 1);
+    }
+    return total;
+}
+
 function calcGrantTotal(numberRows: number[][], ops: string[]): number {
     let total: number = 0;
     const cols = numberRows[0].length;
@@ -30,4 +74,4 @@ function calcGrantTotal(numberRows: number[][], ops: string[]): number {
         total += result;
     }
     return total;
-}
+}