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程式語言 - LeetCode - C++ - 652. Find Duplicate Subtrees

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題目：


解答：

/**
 * 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> mp;

        auto dfs = [&](this auto&& dfs, TreeNode* n) -> string {
            if (!n) {
                return "#";
            }

            string s = to_string(n->val) + "," + dfs(n->left) + "," + dfs(n->right);

            mp[s] += 1;
            if (mp[s] == 2) {
                ans.push_back(n);
            }

            return s;
        };

        dfs(root);

        return ans;
    }
};