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
代码
class Solution {
public:
vector<TreeNode *> generateTrees(int n) {
if (n == 0) return {};
return *generateTreesDFS(1, n);
}
vector<TreeNode*> *generateTreesDFS(int start, int end) {
vector<TreeNode*> *subTree = new vector<TreeNode*>();
if (start > end) subTree->push_back(NULL);
else {
for (int i = start; i <= end; ++i) {
vector<TreeNode*> *leftSubTree = generateTreesDFS(start, i - 1);
vector<TreeNode*> *rightSubTree = generateTreesDFS(i + 1, end);
for (int j = 0; j < leftSubTree->size(); ++j) {
for (int k = 0; k < rightSubTree->size(); ++k) {
TreeNode *node = new TreeNode(i);
node->left = (*leftSubTree)[j];
node->right = (*rightSubTree)[k];
subTree->push_back(node);
}
}
}
}
return subTree;
}
};
