from collections import deque
class Codec:
    def serialize(self, root):
        if not root: return ""
        res = []
        queue = deque([root])
        while queue:
            node = queue.popleft()
            if node:
                res.append(str(node.val))
                queue.append(node.left)
                queue.append(node.right)
            else:
                res.append("x")
        return ",".join(res)


    def deserialize(self, data):
        if not data: return None
        nums = data.split(",")
        root = TreeNode(nums[0])
        queue = deque([root])
        
        index = 0
        
        while queue:
            node = queue.popleft()
            index += 1
            if nums[index] != "x":
                node.left = TreeNode(int(nums[index]))
                queue.append(node.left)
            
            index += 1
            if nums[index] != "x":
                node.right = TreeNode(int(nums[index]))
                queue.append(node.right)
        return root