Merge pull request #116 from salehhashemi1992/heap-sort

add heap sort to sort algorithms
TheAlgorithms · Sep 18, 2023 · 810f8fc · 810f8fc
2 parents e967070 + e061398
commit 810f8fc
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diff --git a/Sorting/HeapSort.php b/Sorting/HeapSort.php
@@ -0,0 +1,62 @@
+<?php
+/**
+ * HeapSort Algorithm
+ *
+ * The HeapSort algorithm sorts an array by first transforming the array into a max heap and then
+ * iteratively swapping the maximum element from the heap with the last unsorted element
+ * and "heapifying" the heap again.
+ *
+ * @param array $arr
+ * @return array
+ * @throws \UnexpectedValueException
+ */
+function heapSort(array $arr): array
+{
+    $n = count($arr);
+    if ($n <= 0) {
+        throw new \UnexpectedValueException('Input array must have at least one element.');
+    }
+
+    // Build heap
+    for ($i = $n / 2 - 1; $i >= 0; $i--) {
+        heapify($arr, $n, $i);
+    }
+
+    // Extract elements from heap one by one
+    for ($i = $n - 1; $i >= 0; $i--) {
+        // Swap
+        [$arr[0], $arr[$i]] = [$arr[$i], $arr[0]];
+
+        // Heapify the reduced heap
+        heapify($arr, $i, 0);
+    }
+
+    return $arr;
+}
+
+/**
+ * Ensures that the array satisfies the heap property
+ *
+ * @param array $arr
+ * @param int $n
+ * @param int $i
+ */
+function heapify(array &$arr, int $n, int $i): void
+{
+    $largest = $i;
+    $left = 2 * $i + 1;
+    $right = 2 * $i + 2;
+
+    if ($left < $n && $arr[$left] > $arr[$largest]) {
+        $largest = $left;
+    }
+
+    if ($right < $n && $arr[$right] > $arr[$largest]) {
+        $largest = $right;
+    }
+
+    if ($largest !== $i) {
+        [$arr[$i], $arr[$largest]] = [$arr[$largest], $arr[$i]];
+        heapify($arr, $n, $largest);
+    }
+}
diff --git a/tests/Sorting/SortingTests.php b/tests/Sorting/SortingTests.php
@@ -6,6 +6,7 @@
 require_once __DIR__ . '/../../Sorting/BubbleSort.php';
 require_once __DIR__ . '/../../Sorting/BubbleSort2.php';
 require_once __DIR__ . '/../../Sorting/CountSort.php';
+require_once __DIR__ . '/../../Sorting/HeapSort.php';
 require_once __DIR__ . '/../../Sorting/InsertionSort.php';
 require_once __DIR__ . '/../../Sorting/MergeSort.php';
 require_once __DIR__ . '/../../Sorting/QuickSort.php';
@@ -172,4 +173,29 @@ public function testQuickSortCipher()
         $this->assertEquals($result1, $test1);
         $this->assertEquals($result2, $test2);
     }
+
+    public function testHeapSortPerformance()
+    {
+        $array = range(1, 1000000);
+        shuffle($array);  // Randomize the order
+        $start = microtime(true);
+        heapSort($array);
+        $end = microtime(true);
+        $this->assertLessThan(1, $end - $start);
+    }
+
+    public function testHeapSortCipher()
+    {
+        $firstArray = [20, 16, -5, -8, 6, 12, 2, 4, -3, 9];
+        $expectedResultOne = [-8, -5, -3, 2, 4, 6, 9, 12, 16, 20];
+
+        $secondArray = [-6, 12, 14, 17, 5, 4, -9, 15, 0, -8];
+        $expectedResultTwo = [-9, -8, -6, 0, 4, 5, 12, 14, 15, 17];
+
+        $resultOne = heapSort($firstArray);
+        $resultTwo = heapSort($secondArray);
+
+        $this->assertEquals($expectedResultOne, $resultOne);
+        $this->assertEquals($expectedResultTwo, $resultTwo);
+    }
 }