# Insertion in binary search tree using recursion in scala

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

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