Add Red-Black Tree implementation in PHP to datastructure folder

DataStructures/RedBlackTree/Node.php

@@ -0,0 +1,68 @@
+<?php
+
+namespace DataStructures;
+
+/**
+ * Internal Node class representing a single node in the Red-Black Tree
+ *
+ * @internal
+ */
+class Node
+{
+    const RED   = 'RED';
+    const BLACK = 'BLACK';
+
+    public $value;
+    public $color;
+    public $left;
+    public $right;
+    public $parent;
+
+    /**
+     * Node constructor
+     *
+     * @param mixed $value
+     * @param string $color
+     * @param Node|null $parent
+     */
+    public function __construct($value, $color = self::RED, $parent = null)
+    {
+        $this->value  = $value;
+        $this->color  = $color;
+        $this->parent = $parent;
+        $this->left   = null;
+        $this->right  = null;
+    }
+
+    public function isRed(): bool
+    {
+        return $this->color === self::RED;
+    }
+
+    public function isBlack(): bool
+    {
+        return $this->color === self::BLACK;
+    }
+
+    public function sibling(): ?Node
+    {
+        if ($this->parent === null) return null;
+        return $this->parent->left === $this ? $this->parent->right : $this->parent->left;
+    }
+
+    public function isLeftChild(): bool
+    {
+        return $this->parent !== null && $this->parent->left === $this;
+    }
+
+    public function isRightChild(): bool
+    {
+        return $this->parent !== null && $this->parent->right === $this;
+    }
+
+    public function hasRedChild(): bool
+    {
+        return ($this->left !== null && $this->left->isRed()) ||
+               ($this->right !== null && $this->right->isRed());
+    }
+}