2017-day3:spiraling around a point

2017/day03/main.go

@@ -0,0 +1,123 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+
+	"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)
+
+	if part == 1 {
+		ans := part1(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string) int {
+	inputNum := mathutil.StrToInt(input)
+
+	directions := [][2]int{
+		{0, 1},  // right
+		{-1, 0}, // north
+		{0, -1}, // west
+		{1, 0},  // south
+	}
+
+	coordsToSquareNum := map[[2]int]int{
+		[2]int{0, 0}: 1,
+		[2]int{0, 1}: 2,
+	}
+
+	// @ every step, check left, i.e. see if we can turn right
+	// if it's not in map, turn & move there
+	// otherwise continue adding in same direction
+	directionIndex := 0 // start facing right
+	row, col := 0, 1
+	number := 2
+	for len(coordsToSquareNum) < inputNum {
+		leftDiff := directions[(directionIndex+1)%4]
+		leftCoord := [2]int{row + leftDiff[0], col + leftDiff[1]}
+		if _, ok := coordsToSquareNum[leftCoord]; !ok {
+			// turn left first
+			directionIndex = (directionIndex + 1) % 4
+		}
+		// move to coordinate in front & add it to the map
+		diff := directions[directionIndex]
+		row += diff[0]
+		col += diff[1]
+		next := [2]int{row, col}
+		coordsToSquareNum[next] = number
+		number++ // increment number
+	}
+
+	return mathutil.ManhattanDistance(0, 0, row, col)
+}
+
+func part2(input string) int {
+	inputNum := mathutil.StrToInt(input)
+
+	directions := [][2]int{
+		{0, 1},  // right
+		{-1, 0}, // north
+		{0, -1}, // west
+		{1, 0},  // south
+	}
+
+	allNeighborDiffs := [][2]int{
+		{-1, -1},
+		{-1, 0},
+		{-1, 1},
+		{0, -1},
+		{0, 1},
+		{1, -1},
+		{1, 0},
+		{1, 1},
+	}
+
+	coordsToNeighborSum := map[[2]int]int{
+		[2]int{0, 0}: 1,
+		[2]int{0, 1}: 1,
+	}
+
+	// @ every step, check left, i.e. see if we can turn right
+	// if it's not in map, turn & move there
+	// otherwise continue adding in same direction
+	directionIndex := 0 // start facing right
+	row, col := 0, 1
+	for len(coordsToNeighborSum) < inputNum {
+		leftDiff := directions[(directionIndex+1)%4]
+		leftCoord := [2]int{row + leftDiff[0], col + leftDiff[1]}
+		if _, ok := coordsToNeighborSum[leftCoord]; !ok {
+			// turn left first
+			directionIndex = (directionIndex + 1) % 4
+		}
+		// move to coordinate in front & add it to the map
+		diff := directions[directionIndex]
+		row += diff[0]
+		col += diff[1]
+		next := [2]int{row, col}
+
+		var sum int
+		for _, d := range allNeighborDiffs {
+			sum += coordsToNeighborSum[[2]int{row + d[0], col + d[1]}]
+		}
+
+		if sum > inputNum {
+			return sum
+		}
+
+		coordsToNeighborSum[next] = sum
+	}
+
+	panic("uh something broke, return should occur in for loop")
+}

2017/day03/main_test.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{"actual", util.ReadFile("input.txt"), 326},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_part2(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  int
+	}{
+		{"actual", util.ReadFile("input.txt"), 363010},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part2(tt.input); got != tt.want {
+				t.Errorf("part2() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}