feat: add p2 solution

internal/2015/DayTwo/code.go

@@ -29,5 +29,20 @@ func PartOne(data []string) int {
 }
 
 func PartTwo(data []string) int {
-	return 0
+	total := 0
+	for _, line := range data {
+		parts := strings.Split(line, "x")
+		length, _ := strconv.Atoi(parts[0])
+		width, _ := strconv.Atoi(parts[1])
+		height, _ := strconv.Atoi(parts[2])
+
+		smallest := min(length, width, height)
+		middle := length + width + height - smallest - max(length, width, height)
+
+		perimeter := 2 * (smallest + middle)
+		volume := length * width * height
+
+		total += perimeter + volume
+	}
+	return total
 }

internal/2015/DayTwo/code_test.go

@@ -21,3 +21,23 @@ func TestPartOne(t *testing.T) {
 		})
 	}
 }
+
+func TestPartTwo(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected int
+	}{
+		{"2x3x4", "2x3x4", 34},
+		{"1x1x10", "1x1x10", 14},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := PartTwo([]string{tt.input})
+			if got != tt.expected {
+				t.Errorf("PartTwo(%q) = %d, want %d", tt.input, got, tt.expected)
+			}
+		})
+	}
+}