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Day 4: Over engineered!
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‎README.md‎

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@@ -10,6 +10,7 @@ Each day will be setup as a separate folder.
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- [Day 1](/day-1/) - Historian Hysteria
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- [Day 2](/day-2/) - Red-Nosed Reports
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- [Day 3](/day-3/) - Mull It Over
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- [Day 4](/day-4/) - Ceres Search
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## Environment Setup
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‎day-4/README.md‎

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# Day 4 - Ceres Search
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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 recognize the interior of the Ceres monitoring station!
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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 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 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 might appear, where irrelevant characters have been replaced with .:
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```
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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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```
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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 have been replaced with .:
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```
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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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## 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 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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```
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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 backwards.
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Here's the same example from before, but this time all of the X-MASes have been kept instead:
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```
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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/main.go‎

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package main
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import (
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_ "embed"
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"flag"
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"fmt"
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"log"
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"strings"
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file "github.com/shaunburdick/advent-of-code-2024/lib"
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)
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var input string
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func init() {
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// do this in init (not main) so test file has same input
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inputFile, err := file.LoadRelativeFile("input.txt")
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if err != nil {
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log.Println(err)
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}
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input = strings.TrimRight(inputFile, "\n")
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}
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func main() {
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var part int
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flag.IntVar(&part, "part", 1, "part 1 or 2")
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flag.Parse()
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fmt.Println("Running part", part)
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if part == 1 {
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ans := part1(input)
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fmt.Println("Output:", ans)
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} else {
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ans := part2(input)
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fmt.Println("Output:", ans)
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}
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}
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const MAS = "MAS"
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const XMAS = "X" + MAS
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func part1(input string) int {
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parsed := parseInput(input)
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foundWords := 0
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// start traversing the grid
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for y, row := range parsed {
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for x := range row {
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coord := Coords{x, y}
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foundWords += xmasSearch(parsed, "", coord, AllDirections)
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}
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}
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return foundWords
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}
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func part2(input string) int {
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parsed := parseInput(input)
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grid := Grid{parsed}
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foundMas := 0
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// start traversing the grid
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for y, row := range grid.Data {
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if y == 0 || y == len(grid.Data)-1 {
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// skip edges
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continue
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}
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for x, char := range row {
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if x == 0 || x == len(row)-1 {
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// skip edges
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continue
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}
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if char == 'A' {
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coord := Coords{x, y}
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wing1 := string(grid.CharAt(coord.Direction(NorthWest))) + "A" + string(grid.CharAt(coord.Direction(SouthEast)))
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wing2 := string(grid.CharAt(coord.Direction(NorthEast))) + "A" + string(grid.CharAt(coord.Direction(SouthWest)))
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if (wing1 == "MAS" || wing1 == "SAM") && (wing2 == "MAS" || wing2 == "SAM") {
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foundMas += 1
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}
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}
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}
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}
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return foundMas
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}
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type Grid struct {
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Data []string
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}
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func (g Grid) CharAt(c Coords) rune {
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return rune(g.Data[c.y][c.x])
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}
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type Coords struct {
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x int
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y int
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}
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type Direction int
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const (
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NorthWest Direction = iota
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North
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NorthEast
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West
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East
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SouthWest
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South
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SouthEast
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)
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var AllDirections []Direction = []Direction{
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NorthWest,
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North,
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NorthEast,
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West,
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East,
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SouthWest,
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South,
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SouthEast,
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}
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// Generate a list of valid coordinates from the existing one
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// Will only return valid positive values
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func (c Coords) Directions() []Coords {
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directions := []Coords{}
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for _, dir := range AllDirections {
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newCoord := c.Direction(dir)
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// check for bounds
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if newCoord.x >= 0 && newCoord.y >= 0 {
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directions = append(directions, newCoord)
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}
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}
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return directions
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}
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func (c Coords) Direction(d Direction) Coords {
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switch d {
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case NorthWest:
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return Coords{x: c.x - 1, y: c.y - 1}
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case North:
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return Coords{x: c.x, y: c.y - 1}
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case NorthEast:
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return Coords{x: c.x + 1, y: c.y - 1}
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case West:
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return Coords{x: c.x - 1, y: c.y}
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case East:
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return Coords{x: c.x + 1, y: c.y}
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case SouthWest:
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return Coords{x: c.x - 1, y: c.y + 1}
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case South:
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return Coords{x: c.x, y: c.y + 1}
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case SouthEast:
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return Coords{x: c.x + 1, y: c.y + 1}
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default:
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return c
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}
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}
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func xmasSearch(grid []string, currentWord string, coords Coords, directions []Direction) int {
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foundWords := 0
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newWord := currentWord + string(grid[coords.y][coords.x])
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if newWord == XMAS {
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// we match!
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return 1
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} else if len(newWord) >= len(XMAS) || !strings.HasPrefix(XMAS, newWord) {
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// we don't match!
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return 0
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} else {
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// we partially match, keep looking!
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for _, direction := range directions {
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newCoord := coords.Direction(direction)
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// check for bounds
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if newCoord.x >= 0 && newCoord.y >= 0 && newCoord.y < len(grid) && newCoord.x < len(grid[newCoord.y]) {
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foundWords += xmasSearch(grid, newWord, newCoord, []Direction{direction})
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}
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}
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}
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return foundWords
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}
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func parseInput(input string) (ans []string) {
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return strings.Split(input, "\n")
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}

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