Adding PHP examples

02_selection_sort/php/01_selection_sort.php

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+<?php
+
+function findSmall(array $arr)
+{
+    $smallest = $arr[0];
+    $smallestIndex = 0;
+    for ($i = 0; $i < count($arr); $i++) {
+        if ($arr[$i] < $smallest) {
+            $smallest = $arr[$i];
+            $smallestIndex = $i;
+        }
+    }
+    return $smallestIndex;
+}
+
+function selectionSort(array $arr)
+{
+    $newArr = [];
+    for ($i = 0, $length = count($arr); $i < $length; $i++) {
+        $smallest = findSmall($arr);
+        array_push($newArr, array_splice($arr, $smallest, 1)[0]);
+    }
+    return $newArr;
+}
+
+var_dump(selectionSort([5, 3, 6, 2, 10])); // [2, 3, 5, 6, 10]

03_recursion/php/01_countdown.php

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+<?php
+
+function countdown($i)
+{
+    echo $i;
+    // base case
+    if ($i <= 0) {
+        return;
+    } else {
+        countdown($i - 1);
+    }
+}
+
+countdown(5);

03_recursion/php/02_greet.php

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+<?php
+
+function greet2($name)
+{
+    echo 'how are you, ' . $name . '?';
+}
+
+function bye()
+{
+    echo 'ok bye!';
+}
+
+function greet($name)
+{
+    echo 'hello, ' . $name . '!';
+    greet2($name);
+    echo  'getting ready to say bye...';
+    bye();
+}
+
+greet('adit');

03_recursion/php/03_factorial.php

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+<?php
+
+function fact($x)
+{
+    if ($x === 1) {
+        return 1;
+    }
+    return $x * fact($x - 1);
+}
+
+echo fact(5);

04_quicksort/php/01_loop_sum.php

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+<?php
+
+function sum(array $arr)
+{
+    $total = 0;
+    for ($x = 0; $x < count($arr); $x++) {
+        $total += $arr[$x];
+    }
+  return $total;
+}
+
+echo  sum([1, 2, 3, 4]); // 10

04_quicksort/php/02_recursive_count.php

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+<?php
+
+function sum($list)
+{
+    if (count($list) === 0) {
+        return 0;
+    }
+  return $list[0] + sum(array_splice($list, 1));
+}
+
+echo sum([1, 2, 3, 4]); // 10

04_quicksort/php/03_recursive_count.php

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+<?php
+
+function recursiveCount($list) {
+    if (count($list) === 0) {
+        return 0;
+    }
+  return 1 + recursiveCount(array_splice($list, 1));
+}
+
+echo count([0, 1, 2, 3, 4, 5]); // 6

04_quicksort/php/04_recursive_max.php

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+<?php
+
+function recursiveMax($list) {
+    if (count($list) === 2) {
+        return $list[0] > $list[1] ? $list[0] : $list[1];
+    }
+  $subMax = recursiveMax(array_splice($list, 1));
+  return $list[0] > $subMax ? $list[0] : $subMax;
+}
+
+echo recursiveMax([1, 5, 10, 25, 16, 1]); // 25

04_quicksort/php/05_quicksort.php

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+<?php
+
+function quicksort(array $array) {
+    if (count($array) < 2) {
+        // base case, arrays with 0 or 1 element are already "sorted"
+        return $array;
+    } else {
+        // recursive case
+        $pivot = $array[0];
+        var_dump($array);
+
+        // sub-array of all the elements less than the pivot
+        $less = array_filter(array_slice($array, 1), function($el) use ($pivot) { return $el <= $pivot; });
+
+        // sub-array of all the elements greater than the pivot
+        $greater = array_filter(array_slice($array, 1), function($el) use ($pivot) { return $el > $pivot; });
+        return array_merge(quicksort($less), [$pivot], quicksort($greater));
+  }
+}
+
+var_dump(quicksort([10, 5, 2, 3])); // [2, 3, 5, 10]