feat: solve part two

internal/2017/DayThree/code.go

@@ -46,5 +46,36 @@ func PartOne(data int) int {
 }
 
 func PartTwo(data int) int {
-	return 0
+	grid := make(map[[2]int]int)
+	grid[[2]int{0, 0}] = 1
+
+	directions := [4][2]int{{1, 0}, {0, 1}, {-1, 0}, {0, -1}}
+	x, y := 1, 0
+	directionIdx := 0
+	sideLength := 1
+	stepsInSide := 1
+
+	for {
+		sum := grid[[2]int{x - 1, y - 1}] + grid[[2]int{x - 1, y}] + grid[[2]int{x - 1, y + 1}] +
+			grid[[2]int{x, y - 1}] + grid[[2]int{x, y + 1}] +
+			grid[[2]int{x + 1, y - 1}] + grid[[2]int{x + 1, y}] + grid[[2]int{x + 1, y + 1}]
+
+		if sum > data {
+			return sum
+		}
+
+		grid[[2]int{x, y}] = sum
+
+		if stepsInSide == sideLength {
+			stepsInSide = 0
+			if directionIdx%2 == 1 {
+				sideLength++
+			}
+			directionIdx = (directionIdx + 1) % 4
+		}
+
+		x += directions[directionIdx][0]
+		y += directions[directionIdx][1]
+		stepsInSide++
+	}
 }

internal/2017/DayThree/code_test.go

@@ -39,3 +39,46 @@ func TestPartOne(t *testing.T) {
 		})
 	}
 }
+
+func TestPartTwo(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    int
+		expected int
+	}{
+		{
+			name:     "input 1 returns first value larger than 1",
+			input:    1,
+			expected: 2,
+		},
+		{
+			name:     "input 2 returns first value larger than 2",
+			input:    2,
+			expected: 4,
+		},
+		{
+			name:     "input 4 returns first value larger than 4",
+			input:    4,
+			expected: 5,
+		},
+		{
+			name:     "input 5 returns first value larger than 5",
+			input:    5,
+			expected: 10,
+		},
+		{
+			name:     "input 747 returns first value larger than 747",
+			input:    747,
+			expected: 806,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := PartTwo(tt.input)
+			if got != tt.expected {
+				t.Errorf("PartTwo() = %d, want %d", got, tt.expected)
+			}
+		})
+	}
+}