diff --git a/src/BinaryTree.php b/src/BinaryTree.php
index a83093b..cdb323a 100644
--- a/src/BinaryTree.php
+++ b/src/BinaryTree.php
@@ -16,7 +16,8 @@ public static function sort(array $arr): array
             return [];
         }
         $tree = new Tree($arr[0]);
-        for ($i = 1; $i < count($arr); $i++) {
+        $length = count($arr);
+        for ($i = 1; $i < $length; $i++) {
             $tree->put($arr[$i]);
         }
 
diff --git a/src/Bubblesort.php b/src/Bubblesort.php
index 23062a4..b870699 100644
--- a/src/Bubblesort.php
+++ b/src/Bubblesort.php
@@ -21,11 +21,12 @@ public static function sort(array $arr, String $method = "variant1"): array
      */
     private static function variant1(array $arr): array
     {
+        $length = count($arr);
         /**
          *
          * @var int[] $arr
          */
-        for ($j = count($arr) - 1; $j > 0; $j--) {
+        for ($j = $length - 1; $j > 0; $j--) {
             for ($i = 0; $i < $j; $i++) {
                 if ($arr[$i] > $arr[$i + 1]) {
                     [$arr[$i],  $arr[$i + 1]] = [$arr[$i + 1], $arr[$i]];
@@ -42,8 +43,9 @@ private static function variant1(array $arr): array
      */
     private static function variant2($arr): array
     {
-        for ($i = 0; $i < count($arr); $i++) {
-            for ($j = 0; $j < count($arr); $j++) {
+        $length = count($arr);
+        for ($i = 0; $i < $length; $i++) {
+            for ($j = 0; $j < $length; $j++) {
                 if ($arr[$i] < $arr[$j]) {
                     $tmp = $arr[$i];
                     $arr[$i] = $arr[$j];
@@ -61,8 +63,9 @@ private static function variant2($arr): array
      */
     private static function variant3($arr): array
     {
-        for ($i = 0; $i < count($arr); $i++) {
-            for ($j = $i; $j < count($arr); $j++) {
+        $length = count($arr);
+        for ($i = 0; $i < $length; $i++) {
+            for ($j = $i; $j < $length; $j++) {
                 if ($arr[$i] > $arr[$j]) {
                     $tmp = $arr[$i];
                     $arr[$i] = $arr[$j];
@@ -80,9 +83,10 @@ private static function variant3($arr): array
      */
     private static function variant4($arr): array
     {
+        $length = count($arr);
         do {
             $check = false;
-            for ($i = 0; $i < count($arr) - 1; $i++) {
+            for ($i = 0; $i < $length - 1; $i++) {
                 if ($arr[$i] > $arr[$i + 1]) {
                     $tmp = $arr[$i];
                     $arr[$i] = $arr[$i + 1];
@@ -101,9 +105,10 @@ private static function variant4($arr): array
      */
     private static function variant5($arr): array
     {
+        $length = count($arr);
         do {
             $check = false;
-            for ($i = 0; $i < count($arr) - 1; $i++) {
+            for ($i = 0; $i < $length - 1; $i++) {
                 if ($arr[$i] > $arr[$i + 1]) {
                     [$arr[$i],  $arr[$i + 1]] = [$arr[$i + 1], $arr[$i]];
                     $check = true;
diff --git a/src/InsertionSort.php b/src/InsertionSort.php
index a7a571f..43c30e7 100644
--- a/src/InsertionSort.php
+++ b/src/InsertionSort.php
@@ -20,8 +20,9 @@ public static function sort(array $arr, String $method = "variant1"): array
      */
     private static function variant1(array $arr): array
     {
+        $length = count($arr);
         // iterate over all elements
-        for ($i = 1; $i < count($arr); $i++) {
+        for ($i = 1; $i < $length; $i++) {
             // safe current element of iteration
             $element = $arr[$i];
             // loop over already passed array
@@ -46,12 +47,13 @@ private static function variant1(array $arr): array
      */
     private static function variant2(array $arr): array
     {
+        $length = count($arr);
         // start from the first array and iterate over all
-        for ($i = 0; $i < count($arr); $i++) {
+        for ($i = 0; $i < $length; $i++) {
             // assume the first element is the smallest
             $index = $i;
             // loop over the rest of the array
-            for ($j = $i; $j < count($arr); $j++) {
+            for ($j = $i; $j < $length; $j++) {
                 // check if the current element is smaller
                 if ($arr[$j] < $arr[$index]) {
                     // replace the saved index
diff --git a/src/MergeSort.php b/src/MergeSort.php
index bd76b7c..3f81525 100644
--- a/src/MergeSort.php
+++ b/src/MergeSort.php
@@ -10,10 +10,11 @@ class MergeSort
      */
     public static function sort(array $arr): array
     {
-        if (count($arr) <= 1) {
+        $length = count($arr);
+        if ($length <= 1) {
             return $arr;
         }
-        $middle = (int)(count($arr) / 2);
+        $middle = (int)($length / 2);
         $left = array_splice($arr, 0, $middle);
         $left = self::sort($left);
         $right = self::sort($arr);
@@ -31,7 +32,9 @@ public static function merge(array $left, array $right)
         $i = 0;
         $j = 0;
         $result = [];
-        while ($i < count($left) && $j < count($right)) {
+        $lengthLeft = count($left);
+        $lengthRight = count($right);
+        while ($i < $lengthLeft && $j < $lengthRight) {
             if ($left[$i] < $right[$j]) {
                 $result[] = $left[$i];
                 $i++;
@@ -40,10 +43,10 @@ public static function merge(array $left, array $right)
                 $j++;
             }
         }
-        for (; $i < count($left); $i++) {
+        for (; $i < $lengthLeft; $i++) {
             $result[] = $left[$i];
         }
-        for (; $j < count($right); $j++) {
+        for (; $j < $lengthRight; $j++) {
             $result[] = $right[$j];
         }
 
diff --git a/src/QuickSort.php b/src/QuickSort.php
index fbab25c..5267daf 100644
--- a/src/QuickSort.php
+++ b/src/QuickSort.php
@@ -16,7 +16,8 @@ public static function sort(array $arr): array
         $pivot = $arr[0];
         $right = [];
         $left = [];
-        for ($i = 1; $i < count($arr); $i++) {
+        $length = count($arr);
+        for ($i = 1; $i < $length; $i++) {
             if ($arr[$i] < $pivot) {
                 $right[] = $arr[$i];
             } else {