[leetcode] 572. Subtree of Another Tree

题目

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

思路

递归，首先实现一个isEquals函数用来判断两棵树是否相等，然后将root树的每个节点都和subRoot树使用isEquals判断是否相等，并返回结果。

代码

python版本：

class Solution:
    def isSubtree(self, root: Optional[TreeNode], subRoot: Optional[TreeNode]) -> bool:
        def isEquals(root1, root2):
            if not (root1 and root2):
                return root1 is root2
            return (root1.val == root2.val and isEquals(root1.left, root2.left) and isEquals(root1.right, root2.right))

        if isEquals(root, subRoot):
            return True
        if not root:
            return False
        return self.isSubtree(root.left, subRoot) or self.isSubtree(root.right, subRoot)

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