2017-day11: hex grid version of manhattan distance

2017/day11/main.go

@@ -0,0 +1,76 @@
+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 := hexEd(util.ReadFile("./input.txt"), part)
+	fmt.Println("Output:", ans)
+}
+
+var dirIndices = map[string]int{
+	"n":  0,
+	"ne": 1,
+	"se": 2,
+	"s":  3,
+	"sw": 4,
+	"nw": 5,
+}
+
+func hexEd(input string, part int) int {
+	steps := strings.Split(input, ",")
+	tallyDirections := make([]int, 6)
+	var furthest int // for part 2
+	for _, step := range steps {
+		tallyDirections[dirIndices[step]]++
+		distanceFromStart := getDistanceFromOrigin(tallyDirections)
+		furthest = mathutil.MaxInt(furthest, distanceFromStart)
+	}
+
+	if part == 1 {
+		return getDistanceFromOrigin(tallyDirections)
+	}
+	return furthest
+}
+
+func getDistanceFromOrigin(tally []int) int {
+	// zero out opposite indices, after this, there will be at most 3 positive
+	// values in the slice
+	for i := range tally {
+		if tally[i] != 0 {
+			oppositeIndex := (i + 3) % 6
+			smaller := mathutil.MinInt(tally[oppositeIndex], tally[i])
+			tally[oppositeIndex] -= smaller
+			tally[i] -= smaller
+		}
+	}
+
+	// handle neighbors, which collapse into the current direction
+	// e.g. sw,se == s
+	for i := range tally {
+		toLeft := (i + 5) % 6
+		toRight := (i + 1) % 6
+		if tally[toLeft] > 0 && tally[toRight] > 0 {
+			smaller := mathutil.MinInt(tally[toLeft], tally[toRight])
+			tally[toLeft] -= smaller
+			tally[toRight] -= smaller
+			tally[i] += smaller
+		}
+	}
+
+	distanceFromOrigin := mathutil.SumIntSlice(tally)
+
+	return distanceFromOrigin
+}

2017/day11/main_test.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_hexEd(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		part  int
+		want  int
+	}{
+		{"actual-part1", util.ReadFile("input.txt"), 1, 794},
+		{"actual-part2", util.ReadFile("input.txt"), 2, 1524},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := hexEd(tt.input, tt.part); got != tt.want {
+				t.Errorf("hexEd() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

mathutil/math.go

@@ -35,3 +35,18 @@ func StrToInt(in string) int {
 func IntToStr(in int) string {
 	return strconv.Itoa(in)
 }
+
+func AbsInt(in int) int {
+	if in < 0 {
+		return -in
+	}
+	return in
+}
+
+func SumIntSlice(nums []int) int {
+	var sum int
+	for _, n := range nums {
+		sum += n
+	}
+	return sum
+}