2020 day 3 - simple 2d grid traversal

2020/day03/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"flag"
 	"fmt"
+	"strings"
 
 	"github.com/alexchao26/advent-of-code-go/util"
 )
@@ -15,17 +16,73 @@ func main() {
 
 	if part == 1 {
 		ans := part1(util.ReadFile("./input.txt"))
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
 		fmt.Println("Output:", ans)
 	} else {
 		ans := part2(util.ReadFile("./input.txt"))
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
 		fmt.Println("Output:", ans)
 	}
 }
 
 func part1(input string) int {
-	return 0
+	grid := parseInput(input)
+	return rideSlopes(grid, 3, 1)
 }
 
 func part2(input string) int {
-	return 0
+	grid := parseInput(input)
+
+	slopes := [][2]int{
+		// right, down
+		{1, 1},
+		{3, 1},
+		{5, 1},
+		{7, 1},
+		{1, 2},
+	}
+
+	ans := 1
+	for _, slope := range slopes {
+		ans *= rideSlopes(grid, slope[0], slope[1])
+	}
+
+	return ans
+}
+
+func parseInput(input string) (grid [][]bool) {
+	lines := strings.Split(input, "\n")
+
+	grid = make([][]bool, len(lines))
+	for i, l := range lines {
+		grid[i] = make([]bool, len(l))
+		for j, v := range l {
+			if v == '#' {
+				grid[i][j] = true
+			}
+		}
+	}
+
+	return grid
+}
+
+func rideSlopes(grid [][]bool, right, down int) int {
+	var row, col int
+	var ans int
+
+	for {
+		row += down
+		col += right
+		col %= len(grid[0])
+
+		if row < len(grid) {
+			if grid[row][col] {
+				ans++
+			}
+		} else {
+			break
+		}
+	}
+
+	return ans
 }