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程式語言 - LeetCode - C++ - 95. Unique Binary Search Trees II

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參考資訊：
https://www.cnblogs.com/grandyang/p/4301096.html

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*> generateTrees(int n) {
        auto dfs = [&](this auto&& dfs, int l, int r) -> vector<TreeNode*> {
            if (l > r) {
                return { nullptr };
            }

            vector<TreeNode*> ans;

            for (int i = l; i <= r; ++i) {
                auto lt = dfs(l, i - 1);
                auto rt = dfs(i + 1, r);

                for (auto& left : lt) {
                    for (auto& right : rt) {
                        TreeNode* root = new TreeNode(i);
                        root->left = left;
                        root->right = right;
                        ans.push_back(root);
                    }
                }
            }

            return ans;
        };

        return dfs(1, n);
    }
};