adventofcode/2024/04/main.go

package main

import (
	"fmt"

	"aoc/helper"
)

func main() {
	grid := helper.ReadLinesToStringSlices()

	// part 1
	count := 0
	for y := range grid {
		for x := range grid[0] {
			if grid[y][x] == 'X' || grid[y][x] == 'S' {
				count += findXMAS(grid, x, y)
			}
		}
	}
	fmt.Printf("XMAS count: %d\n", count)

	// part 2
	count = 0
	for y := 1; y < len(grid)-1; y++ { // skip first & last row
		for x := 1; x < len(grid[0])-1; x++ { // skip first & last column
			if grid[y][x] == 'A' {
				count += findCrossMAS(grid, x, y)
			}
		}
	}
	fmt.Printf("X-MAS count: %d\n", count)
}

func findXMAS(grid []string, startX int, startY int) (count int) {
	minX := 0                 // upper and left border is 0
	height := len(grid) - 1   // lower border is len-1 (index start = 0)
	width := len(grid[0]) - 1 // right border is len-1 (index start = 0)

	for _, XMAS := range [2]string{"XMAS", "SAMX"} {
		// horizontal
		if startX+3 <= width {
			found := true
			for i := range 4 {
				if grid[startY][startX+i] != XMAS[i] {
					found = false
					break
				}
			}
			if found {
				count++
			}
		}

		// vertikal
		if startY+3 <= height {
			found := true
			for i := range 4 {
				if grid[startY+i][startX] != XMAS[i] {
					found = false
					break
				}
			}
			if found {
				count++
			}
		}

		// diagonal down right
		if startY+3 <= height && startX+3 <= width {
			found := true
			for i := range 4 {
				if grid[startY+i][startX+i] != XMAS[i] {
					found = false
					break
				}
			}
			if found {
				count++
			}
		}

		// diagonal down left
		if startY+3 <= height && startX-3 >= minX {
			found := true
			for i := range 4 {
				if grid[startY+i][startX-i] != XMAS[i] {
					found = false
					break
				}
			}
			if found {
				count++
			}
		}

	}

	return count
}

func findCrossMAS(grid []string, startX int, startY int) (count int) {
	// check clockwise for
	// M.M
	// .A.
	// S.S
	// then rotate the outer ring clockwise and check again
	for _, searchstring := range [4]string{"MMSS", "SMMS", "SSMM", "MSSM"} {
		found := grid[startY-1][startX-1] == searchstring[0] &&
			grid[startY-1][startX+1] == searchstring[1] &&
			grid[startY+1][startX+1] == searchstring[2] &&
			grid[startY+1][startX-1] == searchstring[3]
		if found {
			return 1
		}
	}

	return 0
}