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227 changes: 37 additions & 190 deletions traversals/binary_tree_traversals.py
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Original file line number Diff line number Diff line change
@@ -1,190 +1,37 @@
"""
This is pure python implementation of tree traversal algorithms
"""
from __future__ import print_function

import queue

try:
raw_input # Python 2
except NameError:
raw_input = input # Python 3


class TreeNode:
def __init__(self, data):
self.data = data
self.right = None
self.left = None


def build_tree():
print("\n********Press N to stop entering at any point of time********\n")
print("Enter the value of the root node: ", end="")
check = raw_input().strip().lower()
if check == 'n':
return None
data = int(check)
q = queue.Queue()
tree_node = TreeNode(data)
q.put(tree_node)
while not q.empty():
node_found = q.get()
print("Enter the left node of %s: " % node_found.data, end="")
check = raw_input().strip().lower()
if check == 'n':
return tree_node
left_data = int(check)
left_node = TreeNode(left_data)
node_found.left = left_node
q.put(left_node)
print("Enter the right node of %s: " % node_found.data, end="")
check = raw_input().strip().lower()
if check == 'n':
return tree_node
right_data = int(check)
right_node = TreeNode(right_data)
node_found.right = right_node
q.put(right_node)


def pre_order(node):
if not isinstance(node, TreeNode) or not node:
return
print(node.data, end=" ")
pre_order(node.left)
pre_order(node.right)


def in_order(node):
if not isinstance(node, TreeNode) or not node:
return
in_order(node.left)
print(node.data, end=" ")
in_order(node.right)


def post_order(node):
if not isinstance(node, TreeNode) or not node:
return
post_order(node.left)
post_order(node.right)
print(node.data, end=" ")


def level_order(node):
if not isinstance(node, TreeNode) or not node:
return
q = queue.Queue()
q.put(node)
while not q.empty():
node_dequeued = q.get()
print(node_dequeued.data, end=" ")
if node_dequeued.left:
q.put(node_dequeued.left)
if node_dequeued.right:
q.put(node_dequeued.right)


def level_order_actual(node):
if not isinstance(node, TreeNode) or not node:
return
q = queue.Queue()
q.put(node)
while not q.empty():
list = []
while not q.empty():
node_dequeued = q.get()
print(node_dequeued.data, end=" ")
if node_dequeued.left:
list.append(node_dequeued.left)
if node_dequeued.right:
list.append(node_dequeued.right)
print()
for node in list:
q.put(node)


# iteration version
def pre_order_iter(node):
if not isinstance(node, TreeNode) or not node:
return
stack = []
n = node
while n or stack:
while n: # start from root node, find its left child
print(n.data, end=" ")
stack.append(n)
n = n.left
# end of while means current node doesn't have left child
n = stack.pop()
# start to traverse its right child
n = n.right


def in_order_iter(node):
if not isinstance(node, TreeNode) or not node:
return
stack = []
n = node
while n or stack:
while n:
stack.append(n)
n = n.left
n = stack.pop()
print(n.data, end=" ")
n = n.right


def post_order_iter(node):
if not isinstance(node, TreeNode) or not node:
return
stack1, stack2 = [], []
n = node
stack1.append(n)
while stack1: # to find the reversed order of post order, store it in stack2
n = stack1.pop()
if n.left:
stack1.append(n.left)
if n.right:
stack1.append(n.right)
stack2.append(n)
while stack2: # pop up from stack2 will be the post order
print(stack2.pop().data, end=" ")


if __name__ == '__main__':
print("\n********* Binary Tree Traversals ************\n")

node = build_tree()
print("\n********* Pre Order Traversal ************")
pre_order(node)
print("\n******************************************\n")

print("\n********* In Order Traversal ************")
in_order(node)
print("\n******************************************\n")

print("\n********* Post Order Traversal ************")
post_order(node)
print("\n******************************************\n")

print("\n********* Level Order Traversal ************")
level_order(node)
print("\n******************************************\n")

print("\n********* Actual Level Order Traversal ************")
level_order_actual(node)
print("\n******************************************\n")

print("\n********* Pre Order Traversal - Iteration Version ************")
pre_order_iter(node)
print("\n******************************************\n")

print("\n********* In Order Traversal - Iteration Version ************")
in_order_iter(node)
print("\n******************************************\n")

print("\n********* Post Order Traversal - Iteration Version ************")
post_order_iter(node)
print("\n******************************************\n")
class Node:
def __init__(self,data):
self.left = None
self.right = None
self.data = data

def inOrder(root):
if root:
inOrder(root.left)
print (root.data)
inOrder(root.right)

def preOrder(root):
if root:
print (root.data)
preOrder(root.left)
preOrder(root.right)

def postOrder(root):
if root:
postOrder(root.left)
postOrder(root.right)
print (root.data)

#making the tree
root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)
root.left.right = Node(5)

print inOrder(root)
#4 2 5 1 3
print preOrder(root)
#1 2 4 5 3
print postOrder(root)
#4 5 2 3 1