# Insertion in binary search tree using recursion in swift

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

``````import Foundation
// Swift 4 program for
// Insertion in binary search tree by using recursion
class TreeNode
{
var data: Int;
var left: TreeNode? ;
var right: TreeNode? ;
init(_ data: Int)
{
self.data = data;
self.left = nil;
self.right = nil;
}
}
class BinarySearchTree
{
var root: TreeNode? ;
init()
{
self.root = nil;
}
// Insert a node element
func insert(_ node: TreeNode? , _ data : Int) -> TreeNode?
{
if (node  != nil)
{
if (node!.data >= data)
{
// When new element is smaller or
// equal to current node
node!.left = self.insert(node!.left, data);
}
else
{
// When new element is higher to current node
node!.right = self.insert(node!.right, data);
}
// important to manage root node
return node;
}
else
{
return TreeNode(data);
}
}
// Display preorder
func preorder(_ node: TreeNode? )
{
if (node  != nil)
{
// Display node value
print(" ", node!.data, terminator: "");
// Visit to left subtree
self.preorder(node!.left);
// Visit to right subtree
self.preorder(node!.right);
}
}
func inorder(_ node: TreeNode? )
{
if (node  != nil)
{
// Visit to left subtree
self.inorder(node!.left);
// Display node value
print(" ", node!.data, terminator: "");
// Visit to right subtree
self.inorder(node!.right);
}
}
func postorder(_ node: TreeNode? )
{
if (node  != nil)
{
// Visit to left subtree
self.postorder(node!.left);
// Visit to right subtree
self.postorder(node!.right);
// Display node value
print(" ", node!.data, terminator: "");
}
}
{
self.root = insert(self.root, data);
}
static func main()
{
let tree: BinarySearchTree = BinarySearchTree();
/*
10
/ \
/   \
4     15
/ \   /
3   5 12
-------------
Build binary search tree
*/
// Display tree nodes
print("Preorder ");
tree.preorder(tree.root);
print("\nInorder ");
tree.inorder(tree.root);
print("\nPostorder ");
tree.postorder(tree.root);
}
}
BinarySearchTree.main();``````

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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