力扣算法题—095不同的二叉搜索树【二叉树】

给定一个整数 n，生成所有由 1 ... n 为节点所组成的二叉搜索树。

示例:

输入: 3
输出:
[
  [1,null,3,2],
  [3,2,null,1],
  [3,1,null,null,2],
  [2,1,3],
  [1,null,2,null,3]
]
解释:
以上的输出对应以下 5 种不同结构的二叉搜索树：

   1         3     3      2      1
           /     /      /       
     3     2     1      1   3      2
    /     /                        
   2     1         2                 3

 1 class Solution {
 2 public:
 3     vector<TreeNode *> generateTrees(int n) {
 4         if (n == 0) return {};
 5         return *generateTreesDFS(1, n);
 6     }
 7     vector<TreeNode*> *generateTreesDFS(int start, int end) {
 8         vector<TreeNode*> *subTree = new vector<TreeNode*>();
 9         if (start > end) subTree->push_back(NULL);
10         else {
11             for (int i = start; i <= end; ++i) {
12                 vector<TreeNode*> *leftSubTree = generateTreesDFS(start, i - 1);
13                 vector<TreeNode*> *rightSubTree = generateTreesDFS(i + 1, end);
14                 for (int j = 0; j < leftSubTree->size(); ++j) {
15                     for (int k = 0; k < rightSubTree->size(); ++k) {
16                         TreeNode *node = new TreeNode(i);
17                         node->left = (*leftSubTree)[j];
18                         node->right = (*rightSubTree)[k];
19                         subTree->push_back(node);
20                     }
21                 }
22             }
23         }
24         return subTree;
25     }
26 };