From 41d9aa9eb50090eaec12c23b498d2c5a21756391 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 18:04:47 +0100
Subject: [PATCH 01/15] initial commit

---
 src/ShellSort.php | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 src/ShellSort.php

diff --git a/src/ShellSort.php b/src/ShellSort.php
new file mode 100644
index 0000000..b390191
--- /dev/null
+++ b/src/ShellSort.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace Src;
+
+class ShellSort
+{
+    /**
+     * @param array<int,float> $arr
+     * @return array<int,float>
+     */
+    public static function sort(array $arr): array
+    {
+        return $arr;
+    }
+}

From f0c798dce5ede9baf6145331f651beb5a763094b Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 19:26:05 +0100
Subject: [PATCH 02/15] implement helper for step sequence calculation

---
 src/ShellSort.php | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index b390191..ee6877d 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -12,4 +12,19 @@ public static function sort(array $arr): array
     {
         return $arr;
     }
+
+    /**
+     * Returns the next step sequence based on the current lenght/step
+     *
+     * @param int $start current step sequence or array length
+     * @return int next lower step sequence
+     */
+    private function stepSequence(int $start): int
+    {
+        $next = 1;
+        while ($start > $new = ($next + 1) * 3) {
+            $next = $new;
+        }
+        return $next;
+    }
 }

From adb1f1ea28575895d1453cfe9d835bc5eeb7616d Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 19:27:26 +0100
Subject: [PATCH 03/15] make helper static

---
 src/ShellSort.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index ee6877d..333b98d 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -19,7 +19,7 @@ public static function sort(array $arr): array
      * @param int $start current step sequence or array length
      * @return int next lower step sequence
      */
-    private function stepSequence(int $start): int
+    private static function stepSequence(int $start): int
     {
         $next = 1;
         while ($start > $new = ($next + 1) * 3) {

From d44691d1c2423b838e18984a9b9239b8866fc4fa Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 19:49:43 +0100
Subject: [PATCH 04/15] add outer iteration logic

---
 src/ShellSort.php | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index 333b98d..d7c95f6 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -10,6 +10,17 @@ class ShellSort
      */
     public static function sort(array $arr): array
     {
+        $length = count($arr);
+        $stepSequence = self::stepSequence($length);
+        do {
+            $stepSequence = self::stepSequence($stepSequence);
+            $columns = (int)$length / $stepSequence;
+            for ($i = 0; $i < $columns; $i++) {
+                for ($j = $i + $stepSequence; $j<$length; $j += $stepSequence) {
+                    // basic insertion sort
+                }
+            }
+        } while ($stepSequence > 1);
         return $arr;
     }
 

From 47afc11a5b75305be0a247df3f0a4bf579c90854 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 19:53:14 +0100
Subject: [PATCH 05/15] add basic insertion sort logic

---
 src/ShellSort.php | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index d7c95f6..55cf4d8 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -17,7 +17,13 @@ public static function sort(array $arr): array
             $columns = (int)$length / $stepSequence;
             for ($i = 0; $i < $columns; $i++) {
                 for ($j = $i + $stepSequence; $j<$length; $j += $stepSequence) {
-                    // basic insertion sort
+                    for ($k = $j - $stepSequence; $k >= $i; $k -= $stepSequence) {
+                        if ($arr[$j] < $arr[$k]) {
+                            $safe = $arr[$k];
+                            $arr[$k] = $arr[$j];
+                            $arr[$j] = $safe;
+                        }
+                    }
                 }
             }
         } while ($stepSequence > 1);

From c09aad0abeed780338b5f3d122b48c0a3deb5f5d Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 20:09:15 +0100
Subject: [PATCH 06/15] remove first stepSequence call to prevent reduction of
 stepSequence initially

---
 src/ShellSort.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index 55cf4d8..d627a2e 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -11,7 +11,7 @@ class ShellSort
     public static function sort(array $arr): array
     {
         $length = count($arr);
-        $stepSequence = self::stepSequence($length);
+        $stepSequence = $length;
         do {
             $stepSequence = self::stepSequence($stepSequence);
             $columns = (int)$length / $stepSequence;

From fa2535b2eaf6008f44ce5988cedbd3404e87bf81 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 20:09:46 +0100
Subject: [PATCH 07/15] fix column int cast

---
 src/ShellSort.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index d627a2e..6a13f7b 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -14,7 +14,7 @@ public static function sort(array $arr): array
         $stepSequence = $length;
         do {
             $stepSequence = self::stepSequence($stepSequence);
-            $columns = (int)$length / $stepSequence;
+            $columns = (int)($length / $stepSequence);
             for ($i = 0; $i < $columns; $i++) {
                 for ($j = $i + $stepSequence; $j<$length; $j += $stepSequence) {
                     for ($k = $j - $stepSequence; $k >= $i; $k -= $stepSequence) {

From 60971ac69a3af280f93f2d2e1984799a158ec552 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 20:50:16 +0100
Subject: [PATCH 08/15] remove column logic and outer loop

---
 src/ShellSort.php | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index 6a13f7b..dbb7e20 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -14,15 +14,12 @@ public static function sort(array $arr): array
         $stepSequence = $length;
         do {
             $stepSequence = self::stepSequence($stepSequence);
-            $columns = (int)($length / $stepSequence);
-            for ($i = 0; $i < $columns; $i++) {
-                for ($j = $i + $stepSequence; $j<$length; $j += $stepSequence) {
-                    for ($k = $j - $stepSequence; $k >= $i; $k -= $stepSequence) {
-                        if ($arr[$j] < $arr[$k]) {
-                            $safe = $arr[$k];
-                            $arr[$k] = $arr[$j];
-                            $arr[$j] = $safe;
-                        }
+            for ($i = 0; $i < $length; $i++) {
+                for ($j = $i - $stepSequence; $j >= 0; $j -= $stepSequence) {
+                    if ($arr[$j] > $arr[$i]) {
+                        $safe = $arr[$j];
+                        $arr[$j] = $arr[$i];
+                        $arr[$i] = $safe;
                     }
                 }
             }

From 2b0a65386802f01969c5d7a28dd256de97a023f6 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 21:41:14 +0100
Subject: [PATCH 09/15] scrap everything and start over

---
 src/ShellSort.php | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index dbb7e20..3003bc7 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -13,16 +13,6 @@ public static function sort(array $arr): array
         $length = count($arr);
         $stepSequence = $length;
         do {
-            $stepSequence = self::stepSequence($stepSequence);
-            for ($i = 0; $i < $length; $i++) {
-                for ($j = $i - $stepSequence; $j >= 0; $j -= $stepSequence) {
-                    if ($arr[$j] > $arr[$i]) {
-                        $safe = $arr[$j];
-                        $arr[$j] = $arr[$i];
-                        $arr[$i] = $safe;
-                    }
-                }
-            }
         } while ($stepSequence > 1);
         return $arr;
     }

From a4d3a5a7cc3074fd75dbbbe4c492565e490903f9 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 21:43:58 +0100
Subject: [PATCH 10/15] iterate over the first elements of the column

---
 src/ShellSort.php | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index 3003bc7..fe5291f 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -12,7 +12,10 @@ public static function sort(array $arr): array
     {
         $length = count($arr);
         $stepSequence = $length;
+        $columns = (int)($length / $stepSequence);
         do {
+            for ($i = 0; $i < $columns; $i++) {
+            }
         } while ($stepSequence > 1);
         return $arr;
     }

From a071b33275db5f2cf7bf433ea332b84628c5c940 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 21:49:47 +0100
Subject: [PATCH 11/15] perform insertion sort in column

starting at the second element of the column and going over all the elements of the columns, sorting them this way
---
 src/ShellSort.php | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index fe5291f..fda97b8 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -15,6 +15,13 @@ public static function sort(array $arr): array
         $columns = (int)($length / $stepSequence);
         do {
             for ($i = 0; $i < $columns; $i++) {
+                for ($j = $i+$stepSequence; $j < $length; $j += $stepSequence) {
+                    for ($k = $j-$stepSequence; $k >= $i; $k -= $stepSequence) {
+                        if ($arr[$j] < $arr[$k]) {
+                            [$arr[$j], $arr[$k]] = [$arr[$k], $arr[$j]];
+                        }
+                    }
+                }
             }
         } while ($stepSequence > 1);
         return $arr;

From 727b12c41dc398d4ebd34690fe70a707295e3a06 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 21:51:12 +0100
Subject: [PATCH 12/15] add reduction of stepSequence

effectively approaching the basic insertion sort but with a more sorted array
---
 src/ShellSort.php | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index fda97b8..b7fd7c0 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -14,6 +14,7 @@ public static function sort(array $arr): array
         $stepSequence = $length;
         $columns = (int)($length / $stepSequence);
         do {
+            $stepSequence = self::stepSequence($stepSequence);
             for ($i = 0; $i < $columns; $i++) {
                 for ($j = $i+$stepSequence; $j < $length; $j += $stepSequence) {
                     for ($k = $j-$stepSequence; $k >= $i; $k -= $stepSequence) {

From d3bdc842551de2cfdf555a47bb4e9ebb71091878 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 22:02:18 +0100
Subject: [PATCH 13/15] move column calculation to correct place

---
 src/ShellSort.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index b7fd7c0..722aa66 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -12,9 +12,9 @@ public static function sort(array $arr): array
     {
         $length = count($arr);
         $stepSequence = $length;
-        $columns = (int)($length / $stepSequence);
         do {
             $stepSequence = self::stepSequence($stepSequence);
+            $columns = (int)($length / $stepSequence);
             for ($i = 0; $i < $columns; $i++) {
                 for ($j = $i+$stepSequence; $j < $length; $j += $stepSequence) {
                     for ($k = $j-$stepSequence; $k >= $i; $k -= $stepSequence) {

From ba59e985daf07c0afc9dddb1d3989a6eb8742227 Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 22:16:01 +0100
Subject: [PATCH 14/15] refactor to correct approach of columns

---
 src/ShellSort.php | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/ShellSort.php b/src/ShellSort.php
index 722aa66..97bcbf6 100644
--- a/src/ShellSort.php
+++ b/src/ShellSort.php
@@ -14,12 +14,11 @@ public static function sort(array $arr): array
         $stepSequence = $length;
         do {
             $stepSequence = self::stepSequence($stepSequence);
-            $columns = (int)($length / $stepSequence);
-            for ($i = 0; $i < $columns; $i++) {
+            for ($i = 0; $i < $stepSequence; $i++) {
                 for ($j = $i+$stepSequence; $j < $length; $j += $stepSequence) {
-                    for ($k = $j-$stepSequence; $k >= $i; $k -= $stepSequence) {
-                        if ($arr[$j] < $arr[$k]) {
-                            [$arr[$j], $arr[$k]] = [$arr[$k], $arr[$j]];
+                    for ($k = $j; $k >= $stepSequence; $k -= $stepSequence) {
+                        if ($arr[$k - $stepSequence] > $arr[$k]) {
+                            [$arr[$k], $arr[$k - $stepSequence]] = [$arr[$k - $stepSequence], $arr[$k]];
                         }
                     }
                 }

From 6cbdbafb5c89f0ac95db54d72d09db0e763b8d7f Mon Sep 17 00:00:00 2001
From: dimitrijjedich <dimitrij@startup-werk.de>
Date: Sat, 21 Dec 2024 22:16:52 +0100
Subject: [PATCH 15/15] add tests for shell sort

---
 tests/ShellSortTest.php | 60 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 tests/ShellSortTest.php

diff --git a/tests/ShellSortTest.php b/tests/ShellSortTest.php
new file mode 100644
index 0000000..3beba15
--- /dev/null
+++ b/tests/ShellSortTest.php
@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+use Src\ShellSort;
+
+final class ShellSortTest extends TestCase
+{
+    #[Test]
+    #[DataProvider('arrayProvider')]
+    public function it_should_return_the_sorted_array($arr): void
+    {
+        $this->assertEquals([1,2,3,4,5,6,7,8,9], ShellSort::sort($arr));
+    }
+
+    /*
+    * @return array
+    */
+    public static function arrayProvider(): array
+    {
+        return [
+        [[1,2,3,4,5,6,7,8,9]],
+        [[9,8,7,6,5,4,3,2,1]],
+        [[1,2,3,9,8,7,6,5,4]],
+        [[9,8,7,1,2,3,4,5,6]],
+        [[9,1,8,2,7,3,6,4,5]],
+        [[1,9,2,8,3,7,4,6,5]],
+        [[6,4,1,8,3,9,2,5,7]],
+    ];
+    }
+
+    #[Test]
+    public function it_should_sort_single_element_array(): void
+    {
+        $this->assertEquals([4], ShellSort::sort([4]));
+    }
+
+    #[Test]
+    public function test_empty_array(): void
+    {
+        $this->assertEquals([], ShellSort::sort([]));
+    }
+
+    #[Test]
+    public function it_should_sort_non_consecutive_numbers_correctly(): void
+    {
+        $this->assertEquals([2,5,6,8,9], ShellSort::sort([5,9,6,2,8]));
+    }
+
+    #[Test]
+    public function it_can_sort_array_with_1000_elements(): void
+    {
+        $random = range(1, 1000);
+        shuffle($random);
+        $this->assertEquals(range(1, 1000), ShellSort::sort($random));
+    }
+}