HackerRank Solutions: Tree: Preorder Traversal

Problem

Complete the  function in the editor below, which has  parameter: a pointer to the root of a binary tree. It must print the values in the tree’s preorder traversal as a single line of space-separated values.

Input Format

Our test code passes the root node of a binary tree to the preOrder function.

Constraints

 Nodes in the tree 

Output Format

Print the tree’s preorder traversal as a single line of space-separated values.

Sample Input

     1
\
2
\
5
/  \
3    6
\
4  

Sample Output

1 2 5 3 4 6 

Explanation

The preorder traversal of the binary tree is printed.

Solution

class Node:
def __init__(self, info): 
self.info = info  
self.left = None  
self.right = None 
self.level = None 
def __str__(self):
return str(self.info) 
class BinarySearchTree:
def __init__(self): 
self.root = None
def create(self, val):  
if self.root == None:
self.root = Node(val)
else:
current = self.root
while True:
if val < current.info:
if current.left:
current = current.left
else:
current.left = Node(val)
break
elif val > current.info:
if current.right:
current = current.right
else:
current.right = Node(val)
break
else:
break
"""
Node is defined as
self.left (the left child of the node)
self.right (the right child of the node)
self.info (the value of the node)
"""
def preOrder(root):
#Write your code here
stack = [root]
sti = 0
while (sti < len(stack)):
currnode = stack[sti]
if currnode.left:
stack.insert(sti+1, currnode.left)
if currnode.right:
stack.insert(sti+2, currnode.right)
elif currnode.right:
stack.insert(sti+1, currnode.right)
sti += 1
for s in stack:
print(s.info, end=' ')