In [1]:

    

class BinaryTreeNode:

    def __init__(self, value):
        self.value = value
        self.left  = None
        self.right = None

    def insert_left(self, value):
        self.left = BinaryTreeNode(value)
        return self.left

    def insert_right(self, value):
        self.right = BinaryTreeNode(value)
        return self.right


    

In [50]:

    

def find_second_largest(tree):
    largest = tree
    second_largest = None
    
    while tree.left is not None or tree.right is not None:        
        if tree.right is not None:
            tree = tree.right
        elif tree.left is not None:
            tree = tree.left
            
        if tree.value > largest.value:
            second_largest, largest = largest, tree
        elif tree.value > second_largest.value:
            second_largest = tree

    print 'I guess that the second largest value is %s' % (second_largest.value)
    return second_largest.value


    

In [51]:

    

tree = BinaryTreeNode(100)
tree.left = BinaryTreeNode(0)
tree.right = BinaryTreeNode(200)

find_second_largest(tree) == 100


    

    




I guess that the second largest value is 100






    
Out[51]:





True

In [52]:

    

tree.right.left = BinaryTreeNode(101)

find_second_largest(tree) == 101


    

    




I guess that the second largest value is 101






    
Out[52]:





True

In [53]:

    

tree.right.right = BinaryTreeNode(300)

find_second_largest(tree) == 200


    

    




I guess that the second largest value is 200






    
Out[53]:





True

In [54]:

    

tree.right.right.left = BinaryTreeNode(201)
tree.right.right.right = BinaryTreeNode(400)
tree.right.right.right.right = BinaryTreeNode(500)
tree.right.right.right.right.left = BinaryTreeNode(401)

find_second_largest(tree) == 401


    

    




I guess that the second largest value is 401






    
Out[54]:





True

In [55]:

    

tree.right.right.right.right.left.right = BinaryTreeNode(402)

find_second_largest(tree) == 402


    

    




I guess that the second largest value is 402






    
Out[55]:





True