day 03

Author: alokmenghrajani

day03/day03.go

@@ -0,0 +1,41 @@
+package day03
+
+import "github.com/alokmenghrajani/adventofcode2020/utils"
+
+func Part1(input []string) uint {
+	grid := utils.Grid(input)
+	return collisions(grid, 3, 1)
+}
+
+func Part2(input []string) uint {
+	grid := utils.Grid(input)
+	deltas := [][]int{
+		{1, 1},
+		{3, 1},
+		{5, 1},
+		{7, 1},
+		{1, 2},
+	}
+	r := uint(1)
+	for _, delta := range deltas {
+		r *= collisions(grid, delta[0], delta[1])
+	}
+	return r
+}
+
+func collisions(grid [][]byte, dx, dy int) uint {
+	x := 0
+	y := 0
+	c := uint(0)
+	cols := len(grid[0])
+	for {
+		x += dx
+		y += dy
+		if y >= len(grid) {
+			return c
+		}
+		if grid[y][x%cols] == '#' {
+			c++
+		}
+	}
+}

day03/day03_test.go

@@ -0,0 +1,40 @@
+package day03
+
+import (
+	"github.com/alecthomas/assert"
+	"testing"
+)
+
+func TestPart1(t *testing.T) {
+	r := Part1([]string{
+		"..##.......",
+		"#...#...#..",
+		".#....#..#.",
+		"..#.#...#.#",
+		".#...##..#.",
+		"..#.##.....",
+		".#.#.#....#",
+		".#........#",
+		"#.##...#...",
+		"#...##....#",
+		".#..#...#.#",
+	})
+	assert.Equal(t, uint(7), r)
+}
+
+func TestPart2(t *testing.T) {
+	r := Part2([]string{
+		"..##.......",
+		"#...#...#..",
+		".#....#..#.",
+		"..#.#...#.#",
+		".#...##..#.",
+		"..#.##.....",
+		".#.#.#....#",
+		".#........#",
+		"#.##...#...",
+		"#...##....#",
+		".#..#...#.#",
+	})
+	assert.Equal(t, uint(336), r)
+}