Leetcode 449. Serialize and Deserialize BST. Python (DFS)

449. Serialize and Deserialize BST

Serialization is converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.

Design an algorithm to serialize and deserialize a binary search tree. There is no restriction on how your serialization/deserialization algorithm should work. You need to ensure that a binary search tree can be serialized to a string, and this string can be deserialized to the original tree structure.

The encoded string should be as compact as possible.

 

Example 1:

Input: root = [2,1,3]
Output: [2,1,3]

Example 2:

Input: root = []
Output: []

 

Constraints:

• The number of nodes in the tree is in the range [0, 104].
• 0 <= Node.val <= 104
• The input tree is guaranteed to be a binary search tree.

Solution :

class Codec:

    def serialize(self, root: Optional[TreeNode]) -> str:
        self.ans = []
        
        def dfs(node):
            if not node: return
            self.ans.append(str(node.val))
            dfs(node.left)
            dfs(node.right)
        
        dfs(root)
        return ",".join(self.ans)
        

    def deserialize(self, data: str) -> Optional[TreeNode]:
        if not data: return None
        ans = [int(d) for d in data.split(",")]
        
        
        def dfs(ans, l, u):
            if not ans: return None
            if not l <= ans[0] <= u : return None
            
            node = ans.pop(0) #O(n)
            root = TreeNode(node)
            
            root.left = dfs(ans, l, root.val)
            root.right = dfs(ans, root.val, u)
            
            return root
        return dfs(ans, -float('inf'), float('inf'))

 Explaination :