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572. Subtree Of Another Tree

Tree Depth-First Search String Matching Binary Tree Hash Function

Problem - Subtree Of Another Tree

Easy

Given the roots of two binary trees root and subRoot, return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise.

A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself.

 

Example 1:

Input: root = [3,4,5,1,2], subRoot = [4,1,2]
Output: true

Example 2:

Input: root = [3,4,5,1,2,null,null,null,null,0], subRoot = [4,1,2]
Output: false

 

Constraints:

  • The number of nodes in the root tree is in the range [1, 2000].
  • The number of nodes in the subRoot tree is in the range [1, 1000].
  • -104 <= root.val <= 104
  • -104 <= subRoot.val <= 104

Solutions

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# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isSubtree(self, root: Optional[TreeNode], subRoot: Optional[TreeNode]) -> bool:
        # dfs approach
        # def check(root1: Optional[TreeNode], root2: Optional[TreeNode]) -> bool:
        #     if root1 is None or root2 is None:
        #         return root1 is root2
        #     return (root1.val == root2.val and check(root1.left, root2.left) and 
        #             check(root1.right, root2.right))

        # if root is None:
        #     return False

        # return (check(root, subRoot) or self.isSubtree(root.left, subRoot) or 
        #         self.isSubtree(root.right, subRoot))

        # Hash Map / String Approach
        def encode(node: Optional[TreeNode]) -> str:
            if node is None:
                return ","
            return f"^{node.val}|{encode(node.left)}|{encode(node.right)}"

        root_str = encode(root)
        subRoot_str = encode(subRoot)

        return subRoot_str in root_str

Submission Stats:

  • Runtime: 7 ms (97.41%)
  • Memory: 18.1 MB (59.00%)