Day 13: part 1

day13/day13.go

@@ -0,0 +1,115 @@
+package day13
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"slices"
+	"strings"
+)
+
+func Solution1(filepath string) int {
+	file, err := os.Open(filepath)
+	if err != nil {
+		log.Fatalf("Failed to open the input file with: %v\n", err.Error())
+	}
+
+	result := 0
+	scanner := bufio.NewScanner(file)
+	var currentMatrix []string
+	for scanner.Scan() {
+		currentLine := scanner.Text()
+
+		if len(currentLine) == 0 {
+			result += calcReflection(currentMatrix)
+			currentMatrix = make([]string, 0)
+			continue
+		}
+
+		currentMatrix = append(currentMatrix, currentLine)
+	}
+	if len(currentMatrix) != 0 {
+		result += calcReflection(currentMatrix)
+	}
+	if err = scanner.Err(); err != nil {
+		log.Fatalf("Error during input file read: %v\n", err.Error())
+	}
+
+	return result
+}
+
+func Solution2(filepath string) int {
+	return -1
+}
+
+func calcReflection(m []string) int {
+	// vertical reflection line
+	for i := 1; i < len(m); i++ {
+		step := 0
+		for {
+			// imaginary reflection line is between upIdx=i-1 and downIdx=i, then we start with offset 0 and just keep increasing it by 1 on each iteration
+			// we keep walking until:
+			// a) success - we've reached one of the ends => return
+			// b) failure - we've encountered m[upIdx] != m[downIdx] => break and move onto the next i
+			upIdx := i - 1 - step
+			downIdx := i + step
+
+			if upIdx < 0 || downIdx >= len(m) {
+				// i == number of rows above the current i
+				separator := strings.Repeat("-", len(m[0]))
+				m = slices.Insert(m, i, separator)
+				printMatrix(m)
+				return 100 * i
+			}
+
+			if m[upIdx] != m[downIdx] {
+				fmt.Printf("i=%d, step=%d: %s != %s\n", i, step, m[upIdx], m[downIdx])
+				break
+			}
+			step++
+		}
+	}
+
+	// horizontal reflection line
+	for i := 1; i < len(m[0]); i++ {
+		step := 0
+		for {
+			leftIdx := i - 1 - step
+			rightIdx := i + step
+
+			if leftIdx < 0 || rightIdx >= len(m[0]) {
+				separator := "|"
+				for j := 0; j < len(m); j++ {
+					m[j] = m[j][:i] + separator + m[j][i:]
+				}
+				printMatrix(m)
+				// i == number of cols left of i
+				return i
+			}
+
+			reflection := true
+			for j := 0; j < len(m); j++ {
+				currentRow := m[j]
+				if currentRow[leftIdx] != currentRow[rightIdx] {
+					reflection = false
+					break
+				}
+			}
+			if !reflection {
+				break
+			}
+			step++
+		}
+	}
+
+	return 0
+}
+
+func printMatrix(m []string) {
+	fmt.Println("-----MATRIX START-----")
+	for _, row := range m {
+		fmt.Println(row)
+	}
+	fmt.Println("------MATRIX END------")
+}

day13/day13_test.go

@@ -0,0 +1,23 @@
+package day13
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestSolution1(t *testing.T) {
+	cases := map[string]int{
+		"test_input11": 405,
+		"test_input12": 1600,
+	}
+
+	for input, expectedResult := range cases {
+		result := Solution1(input)
+
+		if result == expectedResult {
+			fmt.Printf("Solution1()=%d, OK\n", result)
+		} else {
+			t.Fatalf("Solution1()=%d, expecting %d, FAIL\n", result, expectedResult)
+		}
+	}
+}

day13/test_input11

@@ -0,0 +1,15 @@
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#

day13/test_input12

@@ -0,0 +1,17 @@
+####.#.#......#
+#.####.#..##.#.
+###.###.###...#
+####.#.##....##
+.###..#.##..###
+#....#....###.#
+#...###..#.....
+##..###..#.....
+#....#....###.#
+.###..#.##..###
+####.#.##....##
+###.###.###...#
+#.####.#..##.#.
+####.#.#......#
+#...#.#.#..#.#.
+#.##.##.#....##
+#.##.##.#....##

main.go

@@ -13,6 +13,7 @@ import (
 	"advent-of-code/day10"
 	"advent-of-code/day11"
 	"advent-of-code/day12"
+	"advent-of-code/day13"
 	"fmt"
 	"time"
 )
@@ -60,4 +61,7 @@ func main() {
 
 	runSolution(12, 1, func() int { return day12.Solution1("inputs/day12") })
 	runSolution(12, 2, func() int { return day12.Solution2("inputs/day12") })
+
+	runSolution(13, 1, func() int { return day13.Solution1("inputs/day13") })
+	runSolution(13, 2, func() int { return day13.Solution2("inputs/day13") })
 }