Unique Binary Search Trees II

Description:
Given n, generate all structurally unique BST’s (binary search trees) that store values 1…n.
For example, Given n = 3, your program should return all 5 unique BST’s shown below.

分析：找到一个根节点，剩余的数分别划分为左右子树。

代码：

#include <iostream>#include <vector>#define Elementype intusing namespace std;typedef struct TreeNode //树结点{    Elementype  val;    TreeNode *left;    TreeNode *right;    TreeNode(Elementype x) : val(x), left(nullptr), right(nullptr) {}} *Tree;vector<Tree> BuildTree(int start, int end){       vector<Tree> tree;    if (start > end)    {        tree.push_back(nullptr);    }    for (int k = start; k <= end; k++)    {        vector<Tree>leftTree = BuildTree(start, k - 1);        vector<Tree>rightTree = BuildTree(k + 1, end);        for (auto i : leftTree)        {            for (auto j : rightTree)            {                Tree root = new TreeNode(k);                root->left = i;                root->right = j;                tree.push_back(root);            }        }    }    return tree;}int main(){    int n;    cout << "请输入整数n: ";    cin >> n;    cout << "输出根节点: " << endl;    vector<Tree> result = BuildTree(1,n);    for (auto it = result.begin(); it != result.end(); it++)        cout << (*it)->val << " ";    cout << endl;    system("pause");    return 0;}

测试：