<p>Given an integer <code>n</code>, return <em>all the structurally unique <strong>BST&#39;</strong>s (binary search trees), which has exactly </em><code>n</code><em> nodes of unique values from</em> <code>1</code> <em>to</em> <code>n</code>. Return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/01/18/uniquebstn3.jpg" style="width: 600px; height: 148px;" />
<pre>
<strong>Input:</strong> n = 3
<strong>Output:</strong> [[1,null,2,null,3],[1,null,3,2],[2,1,3],[3,1,null,null,2],[3,2,null,1]]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> [[1]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 8</code></li>
</ul>

/**
 * 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) {}
 * };
 */
const int len = 10; 
vector<vector<TreeNode*>> dp(len, vector<TreeNode*>(0));

class Solution {
private:
    TreeNode* deepcpy(TreeNode* node, int adj = 0){
        if (!node) return node;
        TreeNode* newNode = new TreeNode(node->val + adj);
        newNode->left = deepcpy(node->left, adj);
        newNode->right = deepcpy(node->right, adj);
        return newNode;
    }

public:
    vector<TreeNode*> generateTrees(int n) {
        if (!n) return {NULL};
        if (dp[n].size()) return dp[n];
        vector<TreeNode*> res;
        for (int i=1; i <= n; i++){
            vector<TreeNode*> left = generateTrees(i-1);
            vector<TreeNode*> right = generateTrees(n-i);
            for (auto l: left){
                for (auto r: right){
                    TreeNode* node = new TreeNode(i);
                    node->left = deepcpy(l);
                    node->right = deepcpy(r, i);
                    res.push_back(node);
                }
            }
            // node->left = deepcpy(left);
            // node->right = deepcpy(right, i);
            // res.push_back(node);
            // TreeNode* node = new TreeNode(i);
        }
        return dp[n] = res;
    }
};
18200