# Sum of alternate leaf nodes in bst in swift

Swift program for Sum of alternate leaf nodes in bst. Here more solutions.

``````import Foundation
// Swift 4 program for
// Sum of alternate leaf nodes in bst
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? ;
var alternate: Bool;
init()
{
self.root = nil;
self.alternate = false;
}
// Insert a new node element
{
// Create a new node
let node: TreeNode? = TreeNode(data);
if (self.root == nil)
{
// When add first node in bst
self.root = node;
}
else
{
var find: TreeNode? = self.root;
// Add new node to proper position
while (find  != nil)
{
if (find!.data >= data)
{
if (find!.left == nil)
{
// When left child empty
// So add new node here
find!.left = node;
return;
}
else
{
// Otherwise
// Visit to left sub-tree
find = find!.left;
}
}
else
{
if (find!.right == nil)
{
// When right child empty
// So add new node here.
find!.right = node;
return;
}
else
{
// Visit to right sub-tree
find = find!.right;
}
}
}
}
}
func leafSum(_ node: TreeNode? ) -> Int
{
if (node  != nil)
{
if (node!.left == nil &&
node!.right == nil)
{
// Case A
// When node is leaf node.
// Change status.
self.alternate = !self.alternate;
// Check node is alternate or not.
if (self.alternate)
{
// When get alternate node.
return node!.data;
}
}
else
{
// Case B
// When node is internal
// Visit left and right subtree and
// Find alternate node.
return self.leafSum(node!.left) +
self.leafSum(node!.right);
}
}
return 0;
}
func alternateLeafSum() -> Int
{
// Reset alternate leaf node status
self.alternate = false;
return self.leafSum(self.root);
}
static func main()
{
let tree: BinarySearchTree = BinarySearchTree();
/*
Binary search tree
-------------------
5
/  \
/    \
/      \
3        19
/ \     /   \
2   4   8     31
/ \    / \
7   15 25  50
*/
// Test
print(tree.alternateLeafSum());
}
}
BinarySearchTree.main();``````

Output

``34``

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