95. 不同的二叉搜索树 II

题目链接：https://leetcode.cn/problems/unique-binary-search-trees-ii/description/?source=vscode

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

解析：

其实是一道数据结构二叉搜索树入门题，放在这里提醒dfs不要陷入直接搜的困境，还可以分治

/*** 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*> dfs(int l, int r) {if (l > r) return {nullptr};vector<TreeNode*> ret;for (int i = l; i <= r; i++) {vector<TreeNode*> left_trees = dfs(l, i - 1);vector<TreeNode*> right_trees = dfs(i + 1, r);for (int j = 0; j < left_trees.size(); j++) {for (int k = 0; k < right_trees.size(); k++) {TreeNode* root = new TreeNode(i, left_trees[j], right_trees[k]);ret.emplace_back(root);}}}return ret;}vector<TreeNode*> generateTrees(int n) {return dfs(1, n);}
};