# Second largest element in BST in python

Python program for Second largest element in BST. Here mentioned other language solution.

``````#  Python 3 program for
#  Second largest element in BST
class TreeNode :
def __init__(self, data) :
self.data = data
self.left = None
self.right = None

class BinarySearchTree :
def __init__(self) :
self.root = None
self.result = None
self.counter = 0

#  Insert a node element
#  Create a new node
node = TreeNode(data)
if (self.root == None) :
#  When adds a first node in bst
self.root = node
else :
find = self.root
#  Add new node to proper position
while (find != None) :
if (find.data >= data) :
if (find.left == None) :
#  When left child empty
#  So add new node here
find.left = node
return
else :
#  Otherwise
#  Visit left sub-tree
find = find.left

else :
if (find.right == None) :
#  When right child empty
#  So add new node here
find.right = node
return
else :
#  Visit right sub-tree
find = find.right

#  Find second largest element in a binary search tree
def findSecondBig(self, node) :
if (node != None) :
#  Visit to right subtree
self.findSecondBig(node.right)
if (self.counter == 2) :
return

if (self.result == None or
self.result.data > node.data) :
#  Modified counter variable by one
self.counter += 1
self.result = node

#  Visit to left subtree
self.findSecondBig(node.left)

def secondLargest(self) :
if (self.root == None) :
#  When BST are empty
print("Empty Binary Search Tree")
else :
#  Reset value
self.counter = 0
self.result = None
#  Find second largest
self.findSecondBig(self.root)
if (self.result == None or self.counter < 2) :
#  If In case 2nd Largest node are
#  Not exist in binary search tree
print("Second Largest node are not exist")
else :
print("Second largest node : ", self.result.data)

def main() :
tree = BinarySearchTree()
#  Binary Search Tree
#  -------------------
#        7
#       / \
#      /   \
#     4     10
#    / \   / \
#   3   5 8   10
#          \    \
#           9   10
tree.secondLargest()

if __name__ == "__main__": main()``````

Output

``Second largest node :  9``

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