# Insertion in binary search tree using recursion in kotlin

Kotlin program for Insertion in binary search tree using recursion. Here problem description and explanation.

``````// Kotlin program for
// Insertion in binary search tree by using recursion
class TreeNode
{
var data: Int;
var left: TreeNode ? ;
var right: TreeNode ? ;
constructor(data: Int)
{
this.data = data;
this.left = null;
this.right = null;
}
}
class BinarySearchTree
{
var root: TreeNode ? ;
constructor()
{
this.root = null;
}
// Insert a node element
fun addNode(node: TreeNode ? , data : Int): TreeNode ?
{
if (node != null)
{
if (node.data >= data)
{
// When new element is smaller or
// equal to current node
}
else
{
// When new element is higher to current node
}
// important to manage root node
return node;
}
else
{
return TreeNode(data);
}
}
// Display preorder
fun preorder(node: TreeNode ? ): Unit
{
if (node != null)
{
// Display node value
print("  " + node.data);
// Visit to left subtree
this.preorder(node.left);
// Visit to right subtree
this.preorder(node.right);
}
}
fun inorder(node: TreeNode ? ): Unit
{
if (node != null)
{
// Visit to left subtree
this.inorder(node.left);
// Display node value
print("  " + node.data);
// Visit to right subtree
this.inorder(node.right);
}
}
fun postorder(node: TreeNode ? ): Unit
{
if (node != null)
{
// Visit to left subtree
this.postorder(node.left);
// Visit to right subtree
this.postorder(node.right);
// Display node value
print("  " + node.data);
}
}
}
fun main(args: Array < String > ): Unit
{
val tree: BinarySearchTree = BinarySearchTree();
/*
10
/ \
/   \
4     15
/ \   /
3   5 12
-------------
Build binary search tree

*/
// Display tree nodes
println("Preorder ");
tree.preorder(tree.root);
println("\nInorder ");
tree.inorder(tree.root);
println("\nPostorder ");
tree.postorder(tree.root);
}``````

Output

``````Preorder
10  4  3  5  15  12
Inorder
3  4  5  10  12  15
Postorder
3  5  4  12  15  10``````

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