Leetcode Unique Binary Search Trees II

Leetcode Unique Binary Search Trees II代码，本代码使用c++完成，使用dp方法中的down-up方法，并提供对树的数量的测试。

#include <iostream>#include <unordered_set>#include <vector>#include <string>using namespace std;// Definition for a binary tree node.struct TreeNode {    int val;    TreeNode *left;    TreeNode *right;    TreeNode(int x) : val(x), left(NULL), right(NULL) {}};class Solution {public:    vector<TreeNode*> generateTrees(int n) {        vector<TreeNode*> trees(1, nullptr);        TreeNode *root;        TreeNode *cur;        int end = 0;        for (int i = 1; i <= n; i ++) {            end = trees.size();            for (int j = 0; j < end; j ++) {                root = cloneTree(trees[j]);                cur = root;                TreeNode *newNode = new TreeNode(0);                while(cur != NULL) {                    newNode->left = cur->right;                    cur->right = newNode;                    trees.push_back(cloneTree(root));                    cur->right = newNode->left;                    newNode->left = NULL;                    cur = cur->right;                }                newNode->left = root;                trees[j] = newNode;            }        }        return trees;    }    TreeNode * cloneTree(TreeNode *root) {        if (root == NULL) {            return NULL;        }        TreeNode *cloneRoot = new TreeNode(root->val);        cloneRoot->left = cloneTree(root->left);        cloneRoot->right = cloneTree(root->right);        return cloneRoot;    }};int main() {    Solution * so = new Solution();    vector<TreeNode*> a = so->generateTrees(1);    cout<<"numer: 1"<<", result: "<<a.size()<<endl;    a = so->generateTrees(4);    cout<<"numer: 4"<<", result: "<<a.size()<<endl;    a = so->generateTrees(5);    cout<<"numer: 5"<<", result: "<<a.size()<<endl;}