day 11 expanding galaxies

2023/day11/main.go

@@ -0,0 +1,116 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/mathy"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(input, 2)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part1(input, 1000000)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string, expansionFactor int) int {
+	grid := parseInput(input)
+
+	// record which rows and cols are empty first
+	emptyRows := map[int]bool{}
+	emptyCols := map[int]bool{}
+
+	for r := 0; r < len(grid); r++ {
+		galaxyFound := false
+		for c := 0; c < len(grid[0]); c++ {
+			if grid[r][c] != "." {
+				galaxyFound = true
+				break
+			}
+		}
+		if !galaxyFound {
+			emptyRows[r] = true
+		}
+	}
+	for c := 0; c < len(grid[0]); c++ {
+		galaxyFound := false
+		for r := 0; r < len(grid); r++ {
+			if grid[r][c] != "." {
+				galaxyFound = true
+				break
+			}
+		}
+		if !galaxyFound {
+			emptyCols[c] = true
+		}
+	}
+
+	// traverse grid and calculate coordinates of each galaxy while accumulating the expanded rows/cols
+	// that can be added into the galaxy's coordinates as they're found
+	galaxyCoords := map[int][2]int{}
+	expandedRowsToAdd := 0
+	for r := 0; r < len(grid); r++ {
+		if emptyRows[r] {
+			expandedRowsToAdd += expansionFactor - 1
+			continue
+		}
+
+		expendedColsToAdd := 0
+		for c := 0; c < len(grid[0]); c++ {
+			if emptyCols[c] {
+				expendedColsToAdd += expansionFactor - 1
+				continue
+			}
+
+			if grid[r][c] == "#" {
+				galaxyCoords[len(galaxyCoords)] = [2]int{
+					r + expandedRowsToAdd,
+					c + expendedColsToAdd,
+				}
+			}
+		}
+	}
+
+	// shortest distance is basically manhattan distance, helper function handles absolute values
+	totalDistance := 0
+	for i := 0; i < len(galaxyCoords); i++ {
+		for j := i + 1; j < len(galaxyCoords); j++ {
+			g1, g2 := galaxyCoords[i], galaxyCoords[j]
+			totalDistance += mathy.ManhattanDistance(g1[0], g1[1], g2[0], g2[1])
+		}
+	}
+
+	return totalDistance
+}
+
+func parseInput(input string) (ans [][]string) {
+	for _, line := range strings.Split(input, "\n") {
+		ans = append(ans, strings.Split(line, ""))
+	}
+	return ans
+}

2023/day11/main_test.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"testing"
+)
+
+var example = `...#......
+.......#..
+#.........
+..........
+......#...
+.#........
+.........#
+..........
+.......#..
+#...#.....`
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name            string
+		input           string
+		expansionFactor int
+		want            int
+	}{
+		{
+			name:            "example",
+			input:           example,
+			expansionFactor: 2,
+			want:            374,
+		},
+		{
+			name:            "actual",
+			input:           input,
+			expansionFactor: 2,
+			want:            9734203,
+		},
+
+		// part 2
+		{
+			name:            "example",
+			input:           example,
+			expansionFactor: 10,
+			want:            1030,
+		},
+		{
+			name:            "example",
+			input:           example,
+			expansionFactor: 100,
+			want:            8410,
+		},
+		{
+			name:            "actual",
+			input:           input,
+			expansionFactor: 1000000,
+			want:            568914596391,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input, tt.expansionFactor); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}