[LeetCode] 297. Serialize and Deserialize Binary Tree

 Problem : https://leetcode.com/problems/serialize-and-deserialize-binary-tree/

Use BFS to serialize and deserialize the tree.

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Codec:

    def serialize(self, root):
        """Encodes a tree to a single string.
        
        :type root: TreeNode
        :rtype: str
        """
        output = []
        
        queue = deque([root])
        
        while queue:
            tmp = deque()
            
            while queue:
                node = queue.popleft()
                if not node:
                    output.append('#')
                else:
                    output.append(str(node.val))
                    tmp.append(node.left)
                    tmp.append(node.right)
                    
            queue = tmp
        
        return ','.join(output) if output[0] != '#' else ''
        

    def deserialize(self, data):
        """Decodes your encoded data to tree.
        
        :type data: str
        :rtype: TreeNode
        """
        
        if not data:
            return None
        
        data = data.split(',')
        
        root = TreeNode(int(data[0]))
        i = 1
        
        queue = deque([root])
        
        while i < len(data):
            tmp = deque()
            
            while queue:
                node = queue.popleft()
                
                if data[i] == '#':
                    node.left = None
                else:
                    node.left = TreeNode(int(data[i]))
                    tmp.append(node.left)
                
                i += 1
                
                if data[i] == '#':
                    node.right = None
                else:
                    node.right = TreeNode(int(data[i]))
                    tmp.append(node.right)
                
                i += 1
            
            queue = tmp
        
        return root
                    
        
        

# Your Codec object will be instantiated and called as such:
# ser = Codec()
# deser = Codec()
# ans = deser.deserialize(ser.serialize(root))