652

/**
 * 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 {
unordered_map<string, vector<TreeNode*> > m;
public:
    vector<TreeNode*> findDuplicateSubtrees(TreeNode* root) {
        // Serialize the tree.
        serialize(root);

        // Check if two representations have count more than 1.
        // If so, add it to answer.
        vector<TreeNode*> res;
        for(auto p: m){
            if(p.second.size() > 1)
                res.push_back(p.second[0]);
        }
        return res;
    }

    string serialize(TreeNode *root){
        if(!root) return "#";

        // Get representation of current subtree.
        string repr = "";
        repr = to_string(root->val)+','+serialize(root->left)+','+serialize(root->right);

        // Add root to hash of current representaion.
        m[repr].push_back(root);
        return repr;
    }
};