How to Serialize Binary Tree

Question

I went to an interview today where I was asked to serialize a binary tree. I implemented an array-based approach where the children of node i (numbering in level-order trave

Answer 1

I am not using pre-order but I am using BFS. This is a question from leetcode

Majority of people implementation are incorrect when using pre-order: the expected result should be

"[1,2,3,null,null,4,5]", but instead majority people print the output as "[1,2,3,null,null,4,5,null,null]" since they are not counting the levels.

Here is my implementation with the correct result.

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

def serialize(root):
        queue = [(root,0)]
        result = []
        max_level_with_value = 0
        while queue:
            (node,l) = queue.pop(0)
            if node:
                result.append((node.data,l))
                queue.extend([(node.left,l+1),
                              (node.right,l+1)
                              ])
                max_level_with_value = max(max_level_with_value,l)
            else:
                result.append(('null',l))
        filter_redundant(result,max_level_with_value)


def filter_redundant(result,max_level_with_value):
    for v,l in result:
        if l<= max_level_with_value:
            print(v)




root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.right.left = Node(4)
root.right.right = Node(5)
serialize(root)