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Python Program for Depth First Binary Tree Search using Recursion
When it is required to perform depth first search on a tree using recursion, a class is defined, and methods are defined on it that help perform breadth first search.
Below is a demonstration for the same −
Example
class BinaryTree_struct:
def __init__(self, key=None):
self.key = key
self.left = None
self.right = None
def set_root(self, key):
self.key = key
def insert_at_left(self, new_node):
self.left = new_node
def insert_at_right(self, new_node):
self.right = new_node
def search_elem(self, key):
if self.key == key:
return self
if self.left is not None:
temp = self.left.search(key)
if temp is not None:
return temp
if self.right is not None:
temp = self.right.search(key)
return temp
return None
def depth_first_search(self):
print('entering {}...'.format(self.key))
if self.left is not None:
self.left.depth_first_search()
print('at {}...'.format(self.key))
if self.right is not None:
self.right.depth_first_search()
print('leaving {}...'.format(self.key))
btree_instance = None
print('Menu (no duplicate keys)')
print('insert <data> at root')
print('insert <data> left of <data>')
print('insert <data> right of <data>')
print('dfs')
print('quit')
while True:
my_input = input('What would you like to do? ').split()
op = my_input[0].strip().lower()
if op == 'insert':
data = int(my_input[1])
new_node = BinaryTree_struct(data)
sub_op = my_input[2].strip().lower()
if sub_op == 'at':
btree_instance = new_node
else:
position = my_input[4].strip().lower()
key = int(position)
ref_node = None
if btree_instance is not None:
ref_node = btree_instance.search_elem(key)
if ref_node is None:
print('No such key.')
continue
if sub_op == 'left':
ref_node.insert_at_left(new_node)
elif sub_op == 'right':
ref_node.insert_at_right(new_node)
elif op == 'dfs':
print('depth-first search traversal:')
if btree_instance is not None:
btree_instance.depth_first_search()
print()
elif op == 'quit':
break
Output
Menu (no duplicate keys) insert <data> at root insert <data> left of <data> insert <data> right of <data> dfs quit What would you like to do? insert 5 at root What would you like to do? insert 6 left of 5 What would you like to do? insert 8 right of 5 What would you like to do? dfs depth-first search traversal: entering 5... entering 6... at 6... leaving 6... at 5... entering 8... at 8... leaving 8... leaving 5... What would you like to do? quit Use quit() or Ctrl-D (i.e. EOF) to exit
Explanation
The ‘BinaryTree_struct’ class with required attributes is created.
It has an ‘init’ function that is used to assign ‘left’ and ‘right’ nodes to ‘None’.
Another method named ‘set_root’ is defined to specify the root of the tree.
Another method named ‘insert_at_left’ is defined that helps add nodes to the left of the tree.
Another method named ‘insert_at_right’ is defined that helps add nodes to the right of the tree.
Another method named ‘search_elem’ is defined that helps search for a specific element.
A method named ‘depth_first_search’ is defined, that helps perform depth first search on the binary tree.
An instance of the class is created and assigned to ‘None’.
A menu is given.
The user input is taken for the operation that needs to be performed.
Depending on the user’ choice, the operation is performed.
Relevant output is displayed on the console.
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