LeetCode之Unique Binary Search Trees II

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
/*采用类似Unique Binary Search Trees的思路，用递归的方法
求解出所有二叉搜索树。
参考自：https://github.com/soulmachine/leetcode*/
class Solution {
public:
vector<TreeNode*> generateTrees(int n) {
return generateTrees(1, n);
}

vector<TreeNode*> generateTrees(int min_num, int max_num){
vector<TreeNode*> trees;
if(min_num > max_num){
trees.push_back(nullptr);
return trees;
}
for(int k = min_num; k <= max_num; ++k){
vector<TreeNode*> left = generateTrees(min_num, k-1);
vector<TreeNode*> right = generateTrees(k+1, max_num);
for(int i = 0; i < left.size(); ++i){
for(int j = 0; j < right.size(); ++j){
TreeNode* node = new TreeNode(k);
node->left = left[i];
node->right = right[j];
trees.push_back(node);
}
}
}
return trees;
}
};