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‎day-4/README.md‎

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# Day 4: Mull It Over
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<br>
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## Part 1
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"Looks like the Chief's not here. Next!" One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you
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recognize the interior of the [Ceres monitoring station](https://adventofcode.com/2019/day/10)!
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As the search for the Chief continues, a small Elf who lives on the station tugs on your shirt; she'd like to know if you could help her
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with her **word search** (your puzzle input). She only has to find one word: `XMAS`.
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This word search allows words to be horizontal, vertical, diagonal, written backwards, or even overlapping other words. It's a little
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unusual, though, as you don't merely need to find one instance of `XMAS` - you need to find **all of them**. Here are a few ways `XMAS`
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might appear, where irrelevant characters have been replaced with `.`:
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```txt
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..X...
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.SAMX.
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.A..A.
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XMAS.S
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.X....
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```
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The actual word search will be full of letters instead. For example:
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```txt
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MMMSXXMASM
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MSAMXMSMSA
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AMXSXMAAMM
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MSAMASMSMX
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XMASAMXAMM
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XXAMMXXAMA
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SMSMSASXSS
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SAXAMASAAA
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MAMMMXMMMM
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MXMXAXMASX
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```
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In this word search, `XMAS` occurs a total of `18` times; here's the same word search again, but where letters not involved in any `XMAS`
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have been replaced with `.`:
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```txt
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....XXMAS.
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.SAMXMS...
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...S..A...
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..A.A.MS.X
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XMASAMX.MM
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X.....XA.A
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S.S.S.S.SS
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.A.A.A.A.A
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..M.M.M.MM
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.X.X.XMASX
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```
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Take a look at the little Elf's word search. **How many times does `XMAS` appear?**
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<br>
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## Part 2
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The Elf looks quizzically at you. Did you misunderstand the assignment?
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Looking for the instructions, you flip over the word search to find that this isn't actually an `XMAS` puzzle; it's an `X-MAS` puzzle in
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which you're supposed to find two `MAS` in the shape of an `X`. One way to achieve that is like this:
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```txt
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M.S
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.A.
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M.S
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```
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Irrelevant characters have again been replaced with `.` in the above diagram. Within the `X`, each `MAS` can be written forwards or
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backwards.
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Here's the same example from before, but this time all of the `X-MAS`es have been kept instead:
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```txt
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.M.S......
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..A..MSMS.
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.M.S.MAA..
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..A.ASMSM.
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.M.S.M....
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..........
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S.S.S.S.S.
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.A.A.A.A..
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M.M.M.M.M.
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..........
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```
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In this example, an `X-MAS` appears `9` times.
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Flip the word search from the instructions back over to the word search side and try again. **How many times does an `X-MAS` appear?**

‎day-4/day-4.test.ts‎

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import { describe, it } from 'node:test';
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import assert from 'node:assert';
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import path from 'node:path';
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import { countXMASAppearances, countXShapedMASAppearances } from './day-4';
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describe('Day 4: Ceres Search', () => {
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const wordSearchFilePath = path.join(__dirname, 'word-search.txt');
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it('Part 1: should count XMAS appearances', async () => {
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const expectedNumberOfXMASAppearances = 2462; // Verified for this dataset
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const numberOfXMASAppearances = await countXMASAppearances(wordSearchFilePath);
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assert.strictEqual(numberOfXMASAppearances, expectedNumberOfXMASAppearances);
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});
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it('Part 2: should count X-shaped MAS appearances', async () => {
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const expectedNumberOfXShapedMASAppearances = 1877; // Verified for this dataset
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const numberOfXShapedMASAppearances = await countXShapedMASAppearances(wordSearchFilePath);
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assert.strictEqual(numberOfXShapedMASAppearances, expectedNumberOfXShapedMASAppearances);
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});
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});

‎day-4/day-4.ts‎

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import fs from 'node:fs/promises';
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/**
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* Read file
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*/
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const readFile = async (filePath: string): Promise<string> => {
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const fileContents = await fs.readFile(filePath, {
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encoding: 'utf8',
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});
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const normalizedFileContents = fileContents.trim().split(/\r?\n/).join('\n');
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return normalizedFileContents;
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};
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/**
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* Parse word search as grid
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*/
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const parseWordSearchAsGrid = (wordSearchFileContents: string): Array<Array<string>> => {
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// Parse word search string into grid
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// Note: Sadly, we can only parse out a YX grid immediately
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const wordSearchYXGrid = wordSearchFileContents.split('\n').map((wordSearchLine) => {
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return wordSearchLine.split('');
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});
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// Transform YX grid into XY grid (mostly for it to be easier and more understandable to use)
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const wordSearchXYGrid: Array<Array<string>> = [];
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for (let y = 0; y < wordSearchYXGrid.length; y++) {
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for (let x = 0; x < wordSearchYXGrid[y].length; x++) {
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(wordSearchXYGrid[x] ??= [])[y] = wordSearchYXGrid[y][x];
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}
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}
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// Done
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return wordSearchXYGrid;
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};
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/**
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* Part 1: Count XMAS appearances
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*/
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export const countXMASAppearances = async (wordSearchFilePath: string) => {
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// Get data
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const wordSearchFileContents = await readFile(wordSearchFilePath);
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const wordSearchGrid = parseWordSearchAsGrid(wordSearchFileContents);
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// Setup search parameters
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const searchTerm = 'XMAS';
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// Setup all search directions (also covers reverse search terms)
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// Note: Coordinate system starts with 0-0 at top left, search directions run clockwise and start at the top
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const searchOffsets: Array<[x: number, y: number]> = [
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[0, -1], // top
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[1, -1], // top-right
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[1, 0], // right
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[1, 1], // bottom-right
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[0, 1], // bottom
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[-1, 1], // bottom-left
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[-1, 0], // left
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[-1, -1], // top-left
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];
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// Look at each coordinate ...
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const searchTermMatches: Array<Array<[x: number, y: number]>> = [];
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for (let x = 0; x < wordSearchGrid.length; x++) {
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for (let y = 0; y < wordSearchGrid[x].length; y++) {
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// Search into each direction ...
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for (let searchOffsetIndex = 0; searchOffsetIndex < searchOffsets.length; searchOffsetIndex++) {
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// Compare each search term character ...
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const searchTermMatch: Array<[x: number, y: number]> = [];
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for (let searchTermIndex = 0; searchTermIndex < searchTerm.length; searchTermIndex++) {
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// Find current coordinate
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const currentCoordinate: [x: number, y: number] =
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searchTermIndex === 0
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? // Start with original coordinate for first character
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[x, y]
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: // Continue looking at the next coordinate based on previous match and search offset
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[
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searchTermMatch[searchTermMatch.length - 1][0] + searchOffsets[searchOffsetIndex][0],
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searchTermMatch[searchTermMatch.length - 1][1] + searchOffsets[searchOffsetIndex][1],
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];
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// Get character at coordinate
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// Note: Possibly undefined when going "off grid"
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const currentCharacter: string | undefined = wordSearchGrid[currentCoordinate[0]]?.[currentCoordinate[1]];
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// Check whether the character matches the search term
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if (currentCharacter === searchTerm[searchTermIndex]) {
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searchTermMatch.push(currentCoordinate);
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} else {
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break; // Early exit
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}
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}
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// Accept match if all characters have been found
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if (searchTermMatch.length === searchTerm.length) {
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searchTermMatches.push(searchTermMatch);
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}
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}
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}
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}
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const numberOfSearchTermMatches = searchTermMatches.length;
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// !DEBUG: Print each match
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// for (let matchIndex = 0; matchIndex < searchTermMatches.length; matchIndex++) {
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// let searchTermResult = '';
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// for (let coordinateIndex = 0; coordinateIndex < searchTermMatches[matchIndex].length; coordinateIndex++) {
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// searchTermResult +=
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// wordSearchGrid[searchTermMatches[matchIndex][coordinateIndex][0]][searchTermMatches[matchIndex][coordinateIndex][1]];
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// }
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// console.log(searchTermResult);
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// }
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// Done
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return numberOfSearchTermMatches;
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};
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/**
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* Part 1: Count X-shaped MAS appearances
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*/
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export const countXShapedMASAppearances = async (wordSearchFilePath: string) => {
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// Get data
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const wordSearchFileContents = await readFile(wordSearchFilePath);
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const wordSearchGrid = parseWordSearchAsGrid(wordSearchFileContents);
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// Setup search parameters
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const searchTerm = 'MAS';
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// Setup X-shaped search directions (also covers reverse search terms)
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// Note: Coordinate system starts with 0-0 at top left, search directions run clockwise and start at the top-right
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const searchOffsets: Array<[x: number, y: number]> = [
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[1, -1], // top-right
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[1, 1], // bottom-right
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[-1, 1], // bottom-left
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[-1, -1], // top-left
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];
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// Look at each coordinate ...
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const searchTermMatches: Array<Array<[x: number, y: number]>> = [];
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for (let x = 0; x < wordSearchGrid.length; x++) {
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for (let y = 0; y < wordSearchGrid[x].length; y++) {
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// Search into each direction ...
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const searchTermMatchesForSearchOffsets: Array<Array<[x: number, y: number]>> = [];
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for (let searchOffsetIndex = 0; searchOffsetIndex < searchOffsets.length; searchOffsetIndex++) {
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// Compare each search term character ...
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const searchTermMatch: Array<[x: number, y: number]> = [];
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for (let searchTermIndex = 0; searchTermIndex < searchTerm.length; searchTermIndex++) {
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// Find current coordinate
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const currentCoordinate: [x: number, y: number] =
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searchTermIndex === 0
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? // Start with search offset coordinate for first character
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[x + searchOffsets[searchOffsetIndex][0], y + searchOffsets[searchOffsetIndex][1]]
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: // Continue looking at the next coordinate based on previous match and reverse search offset
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[
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searchTermMatch[searchTermMatch.length - 1][0] - searchOffsets[searchOffsetIndex][0],
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searchTermMatch[searchTermMatch.length - 1][1] - searchOffsets[searchOffsetIndex][1],
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];
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// Get character at coordinate
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// Note: Possibly undefined when going "off grid"
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const currentCharacter: string | undefined = wordSearchGrid[currentCoordinate[0]]?.[currentCoordinate[1]];
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// Check whether the character matches the search term
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if (currentCharacter === searchTerm[searchTermIndex]) {
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searchTermMatch.push(currentCoordinate);
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} else {
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break; // Early exit
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}
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}
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// Accept match if all characters have been found
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if (searchTermMatch.length === searchTerm.length) {
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searchTermMatchesForSearchOffsets.push(searchTermMatch);
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}
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}
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// Accept match if two matches along the diagonals (X-shape) have been found
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if (searchTermMatchesForSearchOffsets.length === 2) {
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searchTermMatches.push(searchTermMatchesForSearchOffsets.flat(1));
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}
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}
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}
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const numberOfSearchTermMatches = searchTermMatches.length;
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// !DEBUG: Print each match
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// for (let matchIndex = 0; matchIndex < searchTermMatches.length; matchIndex++) {
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// let searchTermResult = '';
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// for (let coordinateIndex = 0; coordinateIndex < searchTermMatches[matchIndex].length; coordinateIndex++) {
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// searchTermResult +=
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// wordSearchGrid[searchTermMatches[matchIndex][coordinateIndex][0]][searchTermMatches[matchIndex][coordinateIndex][1]];
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// }
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// console.log(searchTermResult);
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// }
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// Done
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return numberOfSearchTermMatches;
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};

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