Set the correct file structure to maintain backward compatibility. (#18)

src/commonMain/kotlin/com.github.adriankuta/datastructure/tree/TreeNode.kt

@@ -0,0 +1,136 @@
+package com.github.adriankuta.datastructure.tree
+
+import com.github.adriankuta.datastructure.tree.TreeNodeIterators.*
+import kotlin.jvm.JvmSynthetic
+
+open class TreeNode<T>(val value: T) : Iterable<TreeNode<T>>, ChildDeclarationInterface<T> {
+
+    private var _parent: TreeNode<T>? = null
+    /**
+     * The converse notion of a child, an immediate ancestor.
+     */
+    val parent: TreeNode<T>?
+        get() = _parent
+
+    private val _children = mutableListOf<TreeNode<T>>()
+    /**
+     * A group of nodes with the same parent.
+     */
+    val children: List<TreeNode<T>>
+        get() = _children
+
+    /**
+     * Choose one of available iterators from [TreeNodeIterators]
+     */
+    var defaultIterator: TreeNodeIterators = PreOrder
+
+    /**
+     * Add new child to current node or root.
+     *
+     * @param child A node which will be directly connected to current node.
+     */
+    fun addChild(child: TreeNode<T>) {
+        child._parent = this
+        _children.add(child)
+    }
+
+    @JvmSynthetic
+    override fun child(value: T, childDeclaration: ChildDeclaration<T>?): TreeNode<T> {
+        val newChild = TreeNode(value)
+        if(childDeclaration != null)
+            newChild.childDeclaration()
+        _children.add(newChild)
+        return newChild
+    }
+
+    /**
+     * Removes a single instance of the specified node from this tree, if it is present.
+     *
+     * @return `true` if the node has been successfully removed; `false` if it was not present in the tree.
+     */
+    fun removeChild(child: TreeNode<T>): Boolean {
+        println(child.value)
+        val removed = child._parent?._children?.remove(child)
+        child._parent = null
+        return removed ?: false
+    }
+
+    /**
+     * This function go through tree and counts children. Root element is not counted.
+     * @return All child and nested child count.
+     */
+    fun nodeCount(): Int {
+        if (_children.isEmpty())
+            return 0
+        return _children.size +
+                _children.sumOf { it.nodeCount() }
+    }
+
+    /**
+     * @return The number of edges on the longest path between current node and a descendant leaf.
+     */
+    fun height(): Int {
+        val childrenMaxDepth = _children.map { it.height() }
+            .maxOrNull()
+            ?: -1 // -1 because this method counts nodes, and edges are always one less then nodes.
+        return childrenMaxDepth + 1
+    }
+
+    /**
+     * Distance is the number of edges along the shortest path between two nodes.
+     * @return The distance between current node and the root.
+     */
+    fun depth(): Int {
+        var depth = 0
+        var tempParent = parent
+
+        while (tempParent != null) {
+            depth++
+            tempParent = tempParent.parent
+        }
+        return depth
+    }
+
+    /**
+     * Remove all children from root and every node in tree.
+     */
+    fun clear() {
+        _parent = null
+        _children.forEach { it.clear() }
+        _children.clear()
+    }
+
+    override fun toString(): String {
+        return value.toString()
+    }
+
+    fun prettyString(): String {
+        val stringBuilder = StringBuilder()
+        print(stringBuilder, "", "")
+        return stringBuilder.toString()
+    }
+
+    private fun print(stringBuilder: StringBuilder, prefix: String, childrenPrefix: String) {
+        stringBuilder.append(prefix)
+        stringBuilder.append(value)
+        stringBuilder.append('\n')
+        val childIterator = _children.iterator()
+        while (childIterator.hasNext()) {
+            val node = childIterator.next()
+            if (childIterator.hasNext()) {
+                node.print(stringBuilder, "$childrenPrefix├── ", "$childrenPrefix│   ")
+            } else {
+                node.print(stringBuilder, "$childrenPrefix└── ", "$childrenPrefix    ")
+            }
+        }
+    }
+
+    /**
+     * You can change default iterator by changing [defaultIterator] property.
+     */
+    override fun iterator(): Iterator<TreeNode<T>> = when (defaultIterator) {
+        PreOrder -> PreOrderTreeIterator(this)
+        PostOrder -> PostOrderTreeIterator(this)
+        LevelOrder -> LevelOrderTreeIterator(this)
+    }
+}