cleanup

2020/day03/main.go

@@ -50,37 +50,23 @@ func part2(input string) int {
 	return ans
 }
 
-func parseInput(input string) (grid [][]bool) {
+func parseInput(input string) (grid [][]string) {
 	lines := strings.Split(input, "\n")
 
-	grid = make([][]bool, len(lines))
+	grid = make([][]string, len(lines))
 	for i, l := range lines {
-		grid[i] = make([]bool, len(l))
-		for j, v := range l {
-			if v == '#' {
-				grid[i][j] = true
-			}
-		}
+		grid[i] = strings.Split(l, "")
 	}
 
 	return grid
 }
 
-func rideSlopes(grid [][]bool, right, down int) int {
-	var row, col int
+func rideSlopes(grid [][]string, right, down int) int {
 	var ans int
 
-	for {
-		row += down
-		col += right
-		col %= len(grid[0])
-
-		if row < len(grid) {
-			if grid[row][col] {
-				ans++
-			}
-		} else {
-			break
+	for row, col := 0, 0; row < len(grid); row, col = row+down, col+right {
+		if grid[row][col%len(grid[0])] == "#" {
+			ans++
 		}
 	}
 

2020/day03/main_test.go

@@ -65,25 +65,3 @@ func TestPart2(t *testing.T) {
 		})
 	}
 }
-
-func Test_rideSlopes(t *testing.T) {
-	type args struct {
-		grid  [][]bool
-		right int
-		down  int
-	}
-	tests := []struct {
-		name string
-		args args
-		want int
-	}{
-		// TODO: Add test cases.
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if got := rideSlopes(tt.args.grid, tt.args.right, tt.args.down); got != tt.want {
-				t.Errorf("rideSlopes() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}

2020/day03/prompt.md

@@ -0,0 +1,92 @@
+
+--- Day 3: Toboggan Trajectory ---
+With the toboggan login problems resolved, you set off toward the airport. While travel by toboggan might be easy, it's certainly not safe: there's very minimal steering and the area is covered in trees. You'll need to see which angles will take you near the fewest trees.
+
+
+Due to the local geology, trees in this area only grow on exact integer coordinates in a grid. You make a map (your puzzle input) of the open squares (.) and trees (#) you can see. For example:
+
+
+..##.......
+#...#...#..
+.#....#..#.
+..#.#...#.#
+.#...##..#.
+..#.##.....
+.#.#.#....#
+.#........#
+#.##...#...
+#...##....#
+.#..#...#.#
+
+
+
+These aren't the only trees, though; due to something you read about once involving arboreal genetics and biome stability, the same pattern repeats to the right many times:
+
+
+..##.........##.........##.........##.........##.........##.......  --->
+#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
+.#....#..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
+..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
+.#...##..#..#...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
+..#.##.......#.##.......#.##.......#.##.......#.##.......#.##.....  --->
+.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
+.#........#.#........#.#........#.#........#.#........#.#........#
+#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...#.##...#...
+#...##....##...##....##...##....##...##....##...##....##...##....#
+.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#.#..#...#.#  --->
+
+
+
+You start on the open square (.) in the top-left corner and need to reach the bottom (below the bottom-most row on your map).
+
+
+The toboggan can only follow a few specific slopes (you opted for a cheaper model that prefers rational numbers); start by counting all the trees you would encounter for the slope right 3, down 1:
+
+
+From your starting position at the top-left, check the position that is right 3 and down 1. Then, check the position that is right 3 and down 1 from there, and so on until you go past the bottom of the map.
+
+
+The locations you'd check in the above example are marked here with O where there was an open square and X where there was a tree:
+
+
+..##.........##.........##.........##.........##.........##.......  --->
+#..O#...#..#...#...#..#...#...#..#...#...#..#...#...#..#...#...#..
+.#....X..#..#....#..#..#....#..#..#....#..#..#....#..#..#....#..#.
+..#.#...#O#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#..#.#...#.#
+.#...##..#..X...##..#..#...##..#..#...##..#..#...##..#..#...##..#.
+..#.##.......#.X#.......#.##.......#.##.......#.##.......#.##.....  --->
+.#.#.#....#.#.#.#.O..#.#.#.#....#.#.#.#....#.#.#.#....#.#.#.#....#
+.#........#.#........X.#........#.#........#.#........#.#........#
+#.##...#...#.##...#...#.X#...#...#.##...#...#.##...#...#.##...#...
+#...##....##...##....##...#X....##...##....##...##....##...##....#
+.#..#...#.#.#..#...#.#.#..#...X.#.#..#...#.#.#..#...#.#.#..#...#.#  --->
+
+
+
+In this example, traversing the map using this slope would cause you to encounter 7 trees.
+
+
+Starting at the top-left corner of your map and following a slope of right 3 and down 1, how many trees would you encounter?
+
+
+--- Part Two ---
+Time to check the rest of the slopes - you need to minimize the probability of a sudden arboreal stop, after all.
+
+
+Determine the number of trees you would encounter if, for each of the following slopes, you start at the top-left corner and traverse the map all the way to the bottom:
+
+
+
+Right 1, down 1.
+Right 3, down 1. (This is the slope you already checked.)
+Right 5, down 1.
+Right 7, down 1.
+Right 1, down 2.
+
+
+
+In the above example, these slopes would find 2, 7, 3, 4, and 2 tree(s) respectively; multiplied together, these produce the answer 336.
+
+
+What do you get if you multiply together the number of trees encountered on each of the listed slopes?
+