297. Serialize and Deserialize Binary Tree

solution.py

from collections import deque

class Codec:

    def serialize(self, root):
        """Encodes a tree to a single string.
        
        :type root: TreeNode
        :rtype: str
        """
        if not root:
            return ""
        
        result = []
        q = deque([root])
        
        
        while(q):
            level_size = len(q)
            
            for _ in range(level_size):
                node = q.popleft()
                result.append(str(node.val) if node else "null")
                if node:
                    q.append(node.left)
                    q.append(node.right)
                
        return ",".join(result)
        
        

    def deserialize(self, data):
        """Decodes your encoded data to tree.
        
        :type data: str
        :rtype: TreeNode
        """
        if not data:
            return
        
        tree = data.split(",")
        root = TreeNode(val=int(tree[0]))
        # because we won't be able to count index if we start with zero
        # left = 2i
        # righ = 2i+1
        i=1
        
        q = deque([root])
        
        while(q):
            node = q.popleft()
            
            if node:
                left = tree[i]
                right = tree[i+1]

                node.left = None if left == 'null' else TreeNode(val=int(left))
                node.right = None if right == 'null' else TreeNode(val=int(right))

                q.append(node.left)
                q.append(node.right)
                
                i+=2
        
        return root