/** * 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: vector<TreeNode*> findDuplicateSubtrees(TreeNode* root) { vector<TreeNode*> ans; unordered_map<string, int> count; encode(root, count, ans); return ans; } private: string encode(TreeNode* root, unordered_map<string, int>& count, vector<TreeNode*>& ans) { if (!root) return ""; const string encoded = to_string(root->val) + "#" + encode(root->left, count, ans) + "#" + encode(root->right, count, ans); if (++count[encoded] == 2) ans.push_back(root); return encoded; } };