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' {
				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, minY := 0, 0       // upper and left border is 0
	maxY := len(grid) - 1    // lower border is len-1 (index start = 0)
	maxX := len(grid[0]) - 1 // right border is len-1 (index start = 0)

	XMAS := "XMAS"

	// horizontal right
	if startX+3 <= maxX { // check for enough space (pos + 3 = 4 characters for "XMAS")
		found := true
		for i := range 4 {
			// check if gridposition at "i" has character for position "i"
			// i=0 -> XMAS[0] -> "X"
			// ..
			// i=3 -> XMAS[3] -> "S"
			if grid[startY][startX+i] != XMAS[i] {
				found = false
				break
			}
		}
		if found {
			count++
		}
	}

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

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

	// vertikal up
	if startY-3 >= minY {
		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 <= maxY && startX+3 <= maxX {
		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 <= maxY && startX-3 >= minX {
		found := true
		for i := range 4 {
			if grid[startY+i][startX-i] != XMAS[i] {
				found = false
				break
			}
		}
		if found {
			count++
		}
	}

	// diagonal up right
	if startY-3 >= minY && startX+3 <= maxX {
		found := true
		for i := range 4 {
			if grid[startY-i][startX+i] != XMAS[i] {
				found = false
				break
			}
		}
		if found {
			count++
		}
	}

	// diagonal up left
	if startY-3 >= minY && 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) {

	// M.S
	// .A.
	// M.S
	found := grid[startY-1][startX-1] == 'M' && grid[startY-1][startX+1] == 'S' &&
		grid[startY+1][startX-1] == 'M' && grid[startY+1][startX+1] == 'S'
	if found {
		count++
	}

	// M.M
	// .A.
	// S.S
	found = grid[startY-1][startX-1] == 'M' && grid[startY-1][startX+1] == 'M' &&
		grid[startY+1][startX-1] == 'S' && grid[startY+1][startX+1] == 'S'
	if found {
		count++
	}

	// S.M
	// .A.
	// S.M
	found = grid[startY-1][startX-1] == 'S' && grid[startY-1][startX+1] == 'M' &&
		grid[startY+1][startX-1] == 'S' && grid[startY+1][startX+1] == 'M'
	if found {
		count++
	}

	// S.S
	// .A.
	// M.M
	found = grid[startY-1][startX-1] == 'S' && grid[startY-1][startX+1] == 'S' &&
		grid[startY+1][startX-1] == 'M' && grid[startY+1][startX+1] == 'M'
	if found {
		count++
	}

	return count
}