advent-of-code-2024/day4/x-mas.go

package main

import (
    "fmt"
    "os"
    "regexp"
    "strings"
)

func check(e error) {
    if e != nil { panic(e) }
}

func rune_matrix(text string) [][]rune {
    lines := strings.Split(text, "\n")
    
    matrix := make([][]rune, len(lines))
	for i := range matrix {
		matrix[i] = make([]rune, 0, len(lines[0]))
	}

    for i, line := range lines {
        for _, c := range []rune(line) {
            matrix[i] = append(matrix[i], c)
        }
    }

    return matrix
}

func rune_matrix_to_string(matrix [][]rune) string {
    lines := make([]string, 0, len(matrix))

    for _, line := range matrix {
        lines = append(lines, string(line))
    }

    return strings.Join(lines, "\n")
}

func transpose(text string) string {
    matrix := rune_matrix(text)

    matrix_T := make([][]rune, len(matrix[0]))
	for i := range matrix[0] {
		matrix_T[i] = make([]rune, len(matrix))
	}
    
    for i := range matrix {
        for j := range matrix[0] {
            matrix_T[j][i] = matrix[i][j]
        }
    }

    return rune_matrix_to_string(matrix_T)
}

func abs(n int) int {
    if n < 0 { return -n }
    return n
}

func shear(text string, offset int) string {
    lines := strings.Split(text, "\n")
    max_len := 0

    // add left padding
    for pad_left := range lines {
        lines[pad_left] = strings.Repeat(" ", abs(pad_left - offset)) + lines[pad_left]
        max_len = max(max_len, len(lines[pad_left]))
    }

    // make square again by adding right padding
    var pad_right int
    for i := range lines {
        pad_right = max_len - len(lines[i])
        lines[i] = lines[i] + strings.Repeat(" ", pad_right)
    }

    return strings.Join(lines, "\n")
}


func main() {

    dat, err := os.ReadFile("data.txt")
    check(err)
    dat_str := string(dat[:len(dat) - 1])

    // split so that overlapping ones are also matched
    r1 := regexp.MustCompile("MAS")
    r2 := regexp.MustCompile("SAM")

    r_nl := regexp.MustCompile("\n")
    offset := r_nl.FindStringIndex(dat_str)[0] - 1

    r_dot := regexp.MustCompile("\\.")

    // increasing left padding + transpose (shear)
    a_replaced_i1 := r1.ReplaceAllString(transpose(shear(dat_str, 0)), "M.S")
    a_replaced_i2 := r2.ReplaceAllString(transpose(shear(dat_str, 0)), "S.M")
    a_replaced_i1 = shear(transpose(a_replaced_i1), offset)
    a_replaced_i2 = shear(transpose(a_replaced_i2), offset)
    //fmt.Println(a_replaced_i1, "\n")
    //fmt.Println(r_dot.FindAllStringIndex(a_replaced_i1, -1), "\n")
    //fmt.Println(a_replaced_i2, "\n")
    //fmt.Println(r_dot.FindAllStringIndex(a_replaced_i2, -1), "\n")
    dot_indices_i := r_dot.FindAllStringIndex(a_replaced_i1, -1)
    dot_indices_i = append(dot_indices_i, r_dot.FindAllStringIndex(a_replaced_i2, -1)...)
    //fmt.Println(dot_indices_i)

    // decreasing left padding + transpose (shear)
    a_replaced_d1 := r1.ReplaceAllString(transpose(shear(dat_str, offset)), "M.S")
    a_replaced_d2 := r2.ReplaceAllString(transpose(shear(dat_str, offset)), "S.M")
    a_replaced_d1 = shear(transpose(a_replaced_d1), 0)
    a_replaced_d2 = shear(transpose(a_replaced_d2), 0)
    //fmt.Println(a_replaced_d1, "\n")
    //fmt.Println(a_replaced_d2, "\n")
    dot_indices_d := r_dot.FindAllStringIndex(a_replaced_d1, -1)
    dot_indices_d = append(dot_indices_d, r_dot.FindAllStringIndex(a_replaced_d2, -1)...)
    //fmt.Println(dot_indices_d)

    // count duplicates
    matches := 0
    for _, elem1 := range dot_indices_i {
        for _, elem2 := range dot_indices_d {
            if elem1[0] == elem2[0] {
                matches++
                break
            }
        }
    }

    fmt.Println(matches)
}