2016-day01: walking/driving around a grid

2016/day01/main.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/mathutil"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	ans := taxicab(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+var dirs = [][2]int{
+	{-1, 0}, // north
+	{0, 1},  // east
+	{1, 0},  // south
+	{0, -1}, // west
+}
+
+func taxicab(input string, part int) int {
+	var dirIndex int // start facing north
+	var row, col int
+
+	visited := map[[2]int]bool{
+		{0, 0}: true,
+	}
+
+	for _, inst := range strings.Split(input, ", ") {
+		var turn string
+		var steps int
+		fmt.Sscanf(inst, "%1s%d", &turn, &steps)
+		if turn == "R" {
+			dirIndex = (dirIndex + 1) % 4
+		} else if turn == "L" {
+			dirIndex = (dirIndex + 3) % 4
+		} else {
+			panic("unhandled turning direction " + turn)
+		}
+
+		for i := 0; i < steps; i++ {
+			// move forward one step at a time
+			row += dirs[dirIndex][0]
+			col += dirs[dirIndex][1]
+			if visited[[2]int{row, col}] && part == 2 {
+				return mathutil.ManhattanDistance(0, 0, row, col)
+			}
+			visited[[2]int{row, col}] = true
+		}
+	}
+
+	return mathutil.ManhattanDistance(0, 0, row, col)
+}

2016/day01/main_test.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_taxicab(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"actual", util.ReadFile("input.txt"), 1, 234},
+		{"actual", util.ReadFile("input.txt"), 2, 113},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := taxicab(tt.input, tt.part); got != tt.want {
+				t.Errorf("taxicab() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}