diff --git a/src/ExecuteDay.php b/src/ExecuteDay.php
index 161aa8b..e94953d 100644
--- a/src/ExecuteDay.php
+++ b/src/ExecuteDay.php
@@ -15,6 +15,7 @@ final class ExecuteDay extends Command
 
     private string $title;
 
+    #[\Override]
     protected function configure(): void
     {
         $this
@@ -24,6 +25,7 @@ final class ExecuteDay extends Command
             ->addArgument('year', InputArgument::OPTIONAL, 'The year', date('y'));
     }
 
+    #[\Override]
     protected function initialize(InputInterface $input, OutputInterface $output): void
     {
         $this->day = $input->getArgument('day');
@@ -36,6 +38,7 @@ final class ExecuteDay extends Command
         $output->writeln(str_repeat('-', strlen($this->title)));
     }
 
+    #[\Override]
     protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $className = sprintf('%s\\Y%d\\Day%d', __NAMESPACE__, $this->year, $this->day);
diff --git a/src/Puzzle.php b/src/Puzzle.php
index 25df428..18e3d6a 100644
--- a/src/Puzzle.php
+++ b/src/Puzzle.php
@@ -10,6 +10,7 @@ use Symfony\Component\Console\Output\OutputInterface;
 
 final class Puzzle extends Command
 {
+    #[\Override]
     protected function configure(): void
     {
         $this
@@ -19,6 +20,7 @@ final class Puzzle extends Command
             ->addArgument('year', InputArgument::OPTIONAL, 'The year', date('y'));
     }
 
+    #[\Override]
     protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $contents = file_get_contents(
diff --git a/src/Solution.php b/src/Solution.php
index 16f3894..b66d451 100644
--- a/src/Solution.php
+++ b/src/Solution.php
@@ -6,13 +6,13 @@ use JetBrains\PhpStorm\ArrayShape;
 
 abstract class Solution
 {
-    public static int|string|null $part1ExampleResult = null;
+    public static null|int|string $part1ExampleResult = null;
 
-    public static int|string|null $part1Result = null;
+    public static null|int|string $part1Result = null;
 
-    public static int|string|null $part2ExampleResult = null;
+    public static null|int|string $part2ExampleResult = null;
 
-    public static int|string|null $part2Result = null;
+    public static null|int|string $part2Result = null;
 
     /**
      * @var bool When false, do not apply the `array_filter` function when the data is loaded.
@@ -89,12 +89,12 @@ abstract class Solution
 
     public function hasData(): bool
     {
-        return !empty($this->data);
+        return $this->data !== null && $this->data !== [];
     }
 
     public function hasExampleData(): bool
     {
-        return !empty($this->exampleData);
+        return $this->exampleData !== [];
     }
 
     /**
diff --git a/src/Utils/Arr.php b/src/Utils/Arr.php
index 4524b32..b24fbd5 100644
--- a/src/Utils/Arr.php
+++ b/src/Utils/Arr.php
@@ -25,7 +25,7 @@ final class Arr
             } else {
                 $values = $depth === 1
                     ? array_values($item)
-                    : static::flatten($item, $depth - 1);
+                    : self::flatten($item, $depth - 1);
 
                 foreach ($values as $value) {
                     $result[] = $value;
diff --git a/src/Y21/Day1.php b/src/Y21/Day1.php
index 4a3ed1b..1f8e018 100644
--- a/src/Y21/Day1.php
+++ b/src/Y21/Day1.php
@@ -6,17 +6,15 @@ use trizz\AdventOfCode\Solution;
 
 final class Day1 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 7;
+    public static null|int|string $part1ExampleResult = 7;
 
-    public static int|string|null $part1Result = 1688;
+    public static null|int|string $part1Result = 1688;
 
-    public static int|string|null $part2ExampleResult = 5;
+    public static null|int|string $part2ExampleResult = 5;
 
-    public static int|string|null $part2Result = 1728;
+    public static null|int|string $part2Result = 1728;
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part1(array $data): int
     {
         $previous = null;
@@ -34,9 +32,7 @@ final class Day1 extends Solution
         return $increases;
     }
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part2(array $data): int
     {
         $previousSum = null;
diff --git a/src/Y21/Day2.php b/src/Y21/Day2.php
index 1550d47..a7f75a6 100644
--- a/src/Y21/Day2.php
+++ b/src/Y21/Day2.php
@@ -6,17 +6,15 @@ use trizz\AdventOfCode\Solution;
 
 final class Day2 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 150;
+    public static null|int|string $part1ExampleResult = 150;
 
-    public static int|string|null $part1Result = 1_654_760;
+    public static null|int|string $part1Result = 1_654_760;
 
-    public static int|string|null $part2ExampleResult = 900;
+    public static null|int|string $part2ExampleResult = 900;
 
-    public static int|string|null $part2Result = 1_956_047_400;
+    public static null|int|string $part2Result = 1_956_047_400;
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part1(array $data): int
     {
         $depth = 0;
@@ -40,9 +38,7 @@ final class Day2 extends Solution
         return $depth * $horizontal;
     }
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part2(array $data): int
     {
         $aim = 0;
diff --git a/src/Y21/Day3.php b/src/Y21/Day3.php
index 7948ab7..de5d659 100644
--- a/src/Y21/Day3.php
+++ b/src/Y21/Day3.php
@@ -6,13 +6,11 @@ use trizz\AdventOfCode\Solution;
 
 final class Day3 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 198;
+    public static null|int|string $part1ExampleResult = 198;
 
-    public static int|string|null $part1Result = 3_309_596;
+    public static null|int|string $part1Result = 3_309_596;
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part1(array $data): int
     {
         $bits = [];
@@ -29,8 +27,8 @@ final class Day3 extends Solution
         $epsilonRate = '';
 
         foreach ($bits as $bit) {
-            $zeros = array_filter($bit, static fn ($value) => $value === '0');
-            $ones = array_filter($bit, static fn ($value) => $value === '1');
+            $zeros = array_filter($bit, static fn ($value): bool => $value === '0');
+            $ones = array_filter($bit, static fn ($value): bool => $value === '1');
 
             $gammaRate .= ($ones > $zeros) ? '1' : '0';
             $epsilonRate .= ($ones < $zeros) ? '1' : '0';
diff --git a/src/Y21/Day4.php b/src/Y21/Day4.php
index 6909854..ab5a028 100644
--- a/src/Y21/Day4.php
+++ b/src/Y21/Day4.php
@@ -6,25 +6,21 @@ use trizz\AdventOfCode\Solution;
 
 final class Day4 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 4512;
+    public static null|int|string $part1ExampleResult = 4512;
 
-    public static int|string|null $part1Result = 60368;
+    public static null|int|string $part1Result = 60368;
 
-    public static int|string|null $part2ExampleResult = 1924;
+    public static null|int|string $part2ExampleResult = 1924;
 
-    public static int|string|null $part2Result = 17435;
+    public static null|int|string $part2Result = 17435;
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part1(array $data): int|string
     {
         return $this->playBingo($data, firstWins: true);
     }
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part2(array $data): int|string
     {
         return $this->playBingo($data, firstWins: false);
@@ -41,7 +37,7 @@ final class Day4 extends Solution
         array_walk_recursive($winningCard, static function (bool $value, int $key) use (&$return): void {
             $return[$key] = $value;
         });
-        $unusedNumbers = array_keys(array_filter($return, static fn (bool $value) => !$value));
+        $unusedNumbers = array_keys(array_filter($return, static fn (bool $value): bool => !$value));
 
         return (int) array_sum($unusedNumbers) * $number;
     }
@@ -56,10 +52,10 @@ final class Day4 extends Solution
     private function explodeNumbers(string $numberList, string $separator): array
     {
         return array_map(
-            static fn ($value) => (int) $value,
+            static fn ($value): int => (int) $value,
             array_filter(
                 explode($separator, $numberList),
-                static fn (string $value) => $value !== ''
+                static fn (string $value): bool => $value !== ''
             )
         );
     }
@@ -96,7 +92,7 @@ final class Day4 extends Solution
             }
 
             $winningCards = $this->checkCards($cards, $finishedCards);
-            if (empty($winningCards)) {
+            if ($winningCards === []) {
                 continue;
             }
 
@@ -129,7 +125,7 @@ final class Day4 extends Solution
     {
         $cards = array_chunk($data, 5);
         foreach ($cards as $card => $rows) {
-            $cards[$card] = array_map(fn ($value) => $this->explodeNumbers($value, ' '), $rows);
+            $cards[$card] = array_map(fn ($value): array => $this->explodeNumbers($value, ' '), $rows);
 
             foreach ($cards[$card] as $row => $number) {
                 $cards[$card][$row] = array_fill_keys(array_values($number), false);
@@ -147,6 +143,7 @@ final class Day4 extends Solution
     private function checkCards(array $cards, array $finishedCards): array
     {
         $winningCards = [];
+
         // Check rows
         /**
          * @var int   $cardIndex
diff --git a/src/Y21/Day6.php b/src/Y21/Day6.php
index e48aa70..4072a31 100644
--- a/src/Y21/Day6.php
+++ b/src/Y21/Day6.php
@@ -7,13 +7,13 @@ use trizz\AdventOfCode\Solution;
 
 final class Day6 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 5934;
+    public static null|int|string $part1ExampleResult = 5934;
 
-    public static int|string|null $part1Result = 350917;
+    public static null|int|string $part1Result = 350917;
 
-    public static int|string|null $part2ExampleResult = 26_984_457_539;
+    public static null|int|string $part2ExampleResult = 26_984_457_539;
 
-    public static int|string|null $part2Result = 1_592_918_715_629;
+    public static null|int|string $part2Result = 1_592_918_715_629;
 
     /**
      * @var int[]
@@ -32,17 +32,13 @@ final class Day6 extends Solution
         0 => 0,
     ];
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part1(array $data): int
     {
         return $this->processPuzzle(80, $data[0]);
     }
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part2(array $data): int
     {
         return $this->processPuzzle(256, $data[0]);
diff --git a/src/Y21/Day7.php b/src/Y21/Day7.php
index df1e845..48d7b12 100644
--- a/src/Y21/Day7.php
+++ b/src/Y21/Day7.php
@@ -6,25 +6,21 @@ use trizz\AdventOfCode\Solution;
 
 final class Day7 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 37;
+    public static null|int|string $part1ExampleResult = 37;
 
-    public static int|string|null $part1Result = 344297;
+    public static null|int|string $part1Result = 344297;
 
-    public static int|string|null $part2ExampleResult = 168;
+    public static null|int|string $part2ExampleResult = 168;
 
-    public static int|string|null $part2Result = 97_164_301;
+    public static null|int|string $part2Result = 97_164_301;
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part1(array $data): int
     {
         return $this->calculateFuel($data[0], forPart2: false);
     }
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part2(array $data): int
     {
         return $this->calculateFuel($data[0], forPart2: true);
@@ -32,7 +28,7 @@ final class Day7 extends Solution
 
     private function calculateFuel(string $data, bool $forPart2 = false): int
     {
-        $crabs = array_map(static fn (string $crab) => (int) $crab, explode(',', $data));
+        $crabs = array_map(static fn (string $crab): int => (int) $crab, explode(',', $data));
 
         /** @psalm-param array{int: int} $fuelPerPosition */
         $fuelPerPosition = [];
diff --git a/src/Y21/Day8.php b/src/Y21/Day8.php
index 8ecadb4..cf831b0 100644
--- a/src/Y21/Day8.php
+++ b/src/Y21/Day8.php
@@ -8,30 +8,28 @@ use trizz\AdventOfCode\Utils\Str;
 
 final class Day8 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 26;
+    public static null|int|string $part1ExampleResult = 26;
 
-    public static int|string|null $part1Result = 397;
+    public static null|int|string $part1Result = 397;
 
-    public static int|string|null $part2ExampleResult = 61229;
+    public static null|int|string $part2ExampleResult = 61229;
 
-    public static int|string|null $part2Result = 1_027_422;
+    public static null|int|string $part2Result = 1_027_422;
 
     private array $digitPatterns;
 
     private array $patternDigits;
 
-    /**
-     * {@inheritdoc}
-     */
+    #[\Override]
     public function part1(array $data): int
     {
         $values = array_map(
-            static fn ($item) => strlen((string) $item),
+            static fn ($item): int => strlen((string) $item),
             Arr::flatten(
                 array_map(
-                    static fn ($item) => explode(' ', $item),
+                    static fn ($item): array => explode(' ', (string) $item),
                     array_map(
-                        static fn ($item) => explode(' | ', $item)[1],
+                        static fn ($item): string => explode(' | ', (string) $item)[1],
                         $data
                     )
                 )
@@ -41,6 +39,7 @@ final class Day8 extends Solution
         return count(array_intersect($values, [2, 4, 3, 7]));
     }
 
+    #[\Override]
     public function part2(array $data): int|string
     {
         $sequences = [];
@@ -80,37 +79,37 @@ final class Day8 extends Solution
         /** @noinspection PackedHashtableOptimizationInspection */
         $findDigit = [
             // 1 is the only one with 2 segments
-            1 => static fn (string $pattern) => strlen($pattern) === 2,
+            1 => static fn (string $pattern): bool => strlen($pattern) === 2,
             // 7 is the only one with 3 segments
-            7 => static fn (string $pattern) => strlen($pattern) === 3,
+            7 => static fn (string $pattern): bool => strlen($pattern) === 3,
             // 4 is the only one with 4 segments
-            4 => static fn (string $pattern) => strlen($pattern) === 4,
+            4 => static fn (string $pattern): bool => strlen($pattern) === 4,
             // 8 is the only one with 7 segments
-            8 => static fn (string $pattern) => strlen($pattern) === 7,
+            8 => static fn (string $pattern): bool => strlen($pattern) === 7,
             // 9 is 6 segments, matches segments for 4
-            9 => fn (string $pattern) => strlen($pattern) === 6 && Str::matchesAll(
+            9 => fn (string $pattern): bool => strlen($pattern) === 6 && Str::matchesAll(
                 $pattern,
                 $this->digitPatterns[4] ?? ''
             ),
             // 0 is 6 segments, matching 1's segments (9 is already out)
-            0 => fn (string $pattern) => strlen($pattern) === 6 && Str::matchesAll(
+            0 => fn (string $pattern): bool => strlen($pattern) === 6 && Str::matchesAll(
                 $pattern,
                 $this->digitPatterns[1] ?? ''
             ),
             // 6 is 6 segments, the only one left
-            6 => static fn (string $pattern) => strlen($pattern) === 6,
+            6 => static fn (string $pattern): bool => strlen($pattern) === 6,
             // 3 is 5 segments and matches 1's segments
-            3 => fn (string $pattern) => strlen($pattern) === 5 && Str::matchesAll(
+            3 => fn (string $pattern): bool => strlen($pattern) === 5 && Str::matchesAll(
                 $pattern,
                 $this->digitPatterns[1] ?? ''
             ),
             // 5 is 5 segments, and 9 has all the segments of 5
-            5 => fn (string $pattern) => strlen($pattern) === 5 && Str::matchesAll(
+            5 => fn (string $pattern): bool => strlen($pattern) === 5 && Str::matchesAll(
                 $this->digitPatterns[9] ?? '',
                 $pattern
             ),
             // 2 is the only one remaining
-            2 => static fn (string $pattern) => true,
+            2 => static fn (string $pattern): bool => true,
         ];
 
         foreach ($findDigit as $digit => $test) {
diff --git a/src/Y22/Day1.php b/src/Y22/Day1.php
index dc74740..4444af5 100644
--- a/src/Y22/Day1.php
+++ b/src/Y22/Day1.php
@@ -6,21 +6,23 @@ use trizz\AdventOfCode\Solution;
 
 final class Day1 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 24000;
+    public static null|int|string $part1ExampleResult = 24000;
 
-    public static int|string|null $part1Result = 72240;
+    public static null|int|string $part1Result = 72240;
 
-    public static int|string|null $part2ExampleResult = 45000;
+    public static null|int|string $part2ExampleResult = 45000;
 
-    public static int|string|null $part2Result = 210957;
+    public static null|int|string $part2Result = 210957;
 
     public bool $filterDataOnLoad = false;
 
+    #[\Override]
     public function part1(array $data): int
     {
         return $this->calculateCalories($data)[0];
     }
 
+    #[\Override]
     public function part2(array $data): int
     {
         $results = $this->calculateCalories($data);
diff --git a/src/Y22/Day2.php b/src/Y22/Day2.php
index a21c387..50b6faf 100644
--- a/src/Y22/Day2.php
+++ b/src/Y22/Day2.php
@@ -7,14 +7,15 @@ use trizz\AdventOfCode\Y22\Day2\RPS;
 
 final class Day2 extends Solution
 {
-    public static int|string|null $part1ExampleResult = 15;
+    public static null|int|string $part1ExampleResult = 15;
 
-    public static int|string|null $part1Result = 10994;
+    public static null|int|string $part1Result = 10994;
 
-    public static int|string|null $part2ExampleResult = 12;
+    public static null|int|string $part2ExampleResult = 12;
 
-    public static int|string|null $part2Result = 12526;
+    public static null|int|string $part2Result = 12526;
 
+    #[\Override]
     public function part1(array $data): int
     {
         $score = 0;
@@ -28,6 +29,7 @@ final class Day2 extends Solution
         return $score;
     }
 
+    #[\Override]
     public function part2(array $data): int
     {
         $score = 0;