In the algorithm section I am here going to share how to get the left view of the binary tree. For that you must know what is binary tree.

Algorithms: Left view of a binary tree.

Binary tree are the tree where one node can have only two child and cannot have more than two.

Left view means what all nodes are visible to you if you see the tree from the left side. Here look at the below tree

Its left view will be

1 2 4

Here is the code for doing that.

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

def left_view(queue, current_level):
   if len(queue) == 0:
       return
   node = queue[0]
   node,level = node[0],node[1]
   queue.pop(0)
   if node.left:
       queue.append([node.left, level+1])
   if node.right:
       queue.append([node.right, level+1])
   if current_level < level: 
       print node.data,
       current_level = current_level + 1
   left_view(queue,current_level)

queue = list()
root = Node(1)
current_level = 0
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)
root.left.left.left = Node(5)
root.left.left.left.left = Node(6)
root.left.left.right = Node(7)
root.right.right = Node(8)
root.right.right.right = Node(9)
root.right.right.right.left = Node(10)
root.right.right.right.left.right = Node(11)
queue.append([root,0])
left_view(queue,-1)
#1 2 4 5 6 11

Suggested books for Algorithms in Python

What we did here:

We reach a node check if it has left element, if it has we put it in queue and then if it has right put right in it and then call left_view again.

In every Iteration it is going to print the first node of level which will be left view. In this way we get the left view of tree.

First node is checked by the current_height and height associated with node in queue. If current height is less than height with node then it is the first node of that level hence print it. 

So in short it is level order traversal with printing the first node of the level as we get it.

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This was left view of binary tree using python.

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