Day 3: Part 1 and 2

three/day_three.go

@@ -0,0 +1,71 @@
+package three
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+type forest struct {
+	trees       [][]bool
+	rows, width int
+}
+
+func (f *forest) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		if f.rows == 0 {
+			f.width = len(scanner.Text())
+		}
+
+		row := make([]bool, f.width)
+		for position, possibleTree := range scanner.Text() {
+			row[position] = (string(possibleTree) == "#")
+		}
+		f.trees = append(f.trees, row)
+		f.rows++
+	}
+
+	return nil
+}
+
+func (f *forest) toboggan(right, down int) int {
+	x, y, trees := 0, 0, 0
+	for y < len(f.trees)-1 {
+		y = y + down
+		x = x + right
+		if x > (f.width - 1) {
+			x = x % f.width
+		}
+
+		if f.trees[y][x] {
+			trees++
+		}
+	}
+
+	return trees
+}
+
+func PartOne() string {
+	forest := forest{}
+	forest.load("three/trees.txt")
+	trees := forest.toboggan(3, 1)
+	return fmt.Sprintf("Found %d trees on right 3, down 1", trees)
+}
+
+func PartTwo() string {
+	forest := forest{}
+	forest.load("three/trees.txt")
+	product := forest.toboggan(1, 1) *
+		forest.toboggan(3, 1) *
+		forest.toboggan(5, 1) *
+		forest.toboggan(7, 1) *
+		forest.toboggan(1, 2)
+	return fmt.Sprintf("Found product %d of trees over 5 runs", product)
+}