feat: completed day 7 for advent of code 2025

2025/cmd/root.go

@@ -15,6 +15,7 @@ import (
 	"cpatino.com/advent-of-code/2025/day04"
 	"cpatino.com/advent-of-code/2025/day05"
 	"cpatino.com/advent-of-code/2025/day06"
+	"cpatino.com/advent-of-code/2025/day07"
 )
 
 var days = map[int]func(string) (any, any){
@@ -24,6 +25,7 @@ var days = map[int]func(string) (any, any){
 	4: day04.Run,
 	5: day05.Run,
 	6: day06.Run,
+	7: day07.Run,
 }
 
 var rootCmd = &cobra.Command{

2025/day07/day07.go

@@ -0,0 +1,120 @@
+package day07
+
+import (
+	"bufio"
+	"os"
+)
+
+type Beam struct {
+	x, y int
+}
+
+type Grid struct {
+	cells [][]rune
+}
+
+func Run(filename string) (any, any) {
+	file, err := os.Open(filename)
+	if err != nil {
+		panic(err)
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	var grid [][]rune
+	startX, startY := -1, -1
+	row := 0
+	for scanner.Scan() {
+		line := scanner.Text()
+		rowRunes := []rune(line)
+		if startX == -1 {
+			for col, ch := range rowRunes {
+				if ch == 'S' {
+					startX, startY = row, col
+				}
+			}
+		}
+		grid = append(grid, rowRunes)
+		row++
+	}
+	if err := scanner.Err(); err != nil {
+		panic(err)
+	}
+	g := Grid{cells: grid}
+	part1 := Part1(&g, startX, startY)
+	part2 := Part2(&g, startX, startY)
+	return part1, part2
+}
+
+func Part1(grid *Grid, startX, startY int) int {
+	visited := make(map[Beam]bool)
+	splits := 0
+
+	queue := []Beam{{startX, startY}}
+	for len(queue) > 0 {
+		pos := queue[0]
+		queue = queue[1:]
+
+		nx, ny := pos.x+1, pos.y
+		if nx < 0 || ny < 0 || nx >= len(grid.cells) || ny >= len(grid.cells[0]) {
+			continue
+		}
+
+		state := Beam{nx, ny}
+		if visited[state] {
+			continue
+		}
+
+		visited[state] = true
+		cell := grid.cells[nx][ny]
+		if cell == '^' {
+			splits++
+			if ny-1 >= 0 {
+				queue = append(queue, Beam{nx, ny - 1})
+			}
+			if ny+1 < len(grid.cells[0]) {
+				queue = append(queue, Beam{nx, ny + 1})
+			}
+		} else {
+			queue = append(queue, Beam{nx, ny})
+		}
+	}
+
+	return splits
+}
+
+func Part2(grid *Grid, startX, startY int) int {
+	memo := make(map[Beam]int)
+
+	var dfs func(x, y int) int
+	dfs = func(x, y int) int {
+		if x < 0 || y < 0 || x >= len(grid.cells) || y >= len(grid.cells[0]) {
+			return 1
+		}
+
+		state := Beam{x, y}
+		if v, ok := memo[state]; ok {
+			return v
+		}
+
+		cell := grid.cells[x][y]
+		if cell == '^' {
+			left, right := 0, 0
+			if y-1 >= 0 {
+				left = dfs(x+1, y-1)
+			}
+			if y+1 < len(grid.cells[0]) {
+				right = dfs(x+1, y+1)
+			}
+			res := left + right
+			memo[state] = res
+			return res
+		}
+
+		res := dfs(x+1, y)
+		memo[state] = res
+		return res
+	}
+
+	return dfs(startX+1, startY)
+}

2025/day07/day07_test.go

@@ -0,0 +1,34 @@
+package day07
+
+import (
+	"os"
+	"testing"
+)
+
+type TestCase struct {
+	FileName string
+	Part1    any
+	Part2    any
+}
+
+func TestDay07(t *testing.T) {
+	tests := []TestCase{
+		{"test.txt", 21, 40},
+		{"input.txt", 1573, 15093663987272},
+	}
+
+	for _, test := range tests {
+		if _, err := os.Stat(test.FileName); os.IsNotExist(err) {
+			t.Fatalf("test file does not exist: %v", test.FileName)
+		}
+
+		part1, part2 := Run(test.FileName)
+		if test.Part1 != nil && part1 != test.Part1 {
+			t.Fatalf("%s: unexpected part1:\nwant:\t%v\ngot:\t%v", test.FileName, test.Part1, part1)
+		}
+
+		if test.Part2 != nil && part2 != test.Part2 {
+			t.Fatalf("%s: unexpected part2:\nwant:\t%v\ngot:\t%v", test.FileName, test.Part2, part2)
+		}
+	}
+}

2025/day07/test.txt

@@ -0,0 +1,16 @@
+.......S.......
+...............
+.......^.......
+...............
+......^.^......
+...............
+.....^.^.^.....
+...............
+....^.^...^....
+...............
+...^.^...^.^...
+...............
+..^...^.....^..
+...............
+.^.^.^.^.^...^.
+...............