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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    bool isSubStructure(TreeNode* A, TreeNode* B) {
        return (A != nullptr && B != nullptr) && (dfs(A, B) || isSubStructure(A->left, B) || isSubStructure(A->right, B));
    }

private:

    bool dfs(TreeNode* A, TreeNode* B) {
        if(B == nullptr) return true;
        if(A == nullptr || A->val != B->val) return false;
        return dfs(A->left, B->left) && dfs(A->right, B->right); 
    } 

};

https://leetcode.cn/problems/shu-de-zi-jie-gou-lcof/