/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<TreeNode*> generateTrees(int n) {
vector<TreeNode*> result;
if (n < 1) {
return result;
}
return generateTreesOfRange(1, n);
}
vector<TreeNode*> generateTreesOfRange(int beg, int end) {
vector<TreeNode*> result;
if (beg > end) {
result.push_back(NULL);
return result;
}
for (int i = beg; i <= end; ++i) {
vector<TreeNode*> leftTrees = generateTreesOfRange(beg, i - 1);
vector<TreeNode*> rightTrees = generateTreesOfRange(i + 1, end);
for (int j = 0; j < leftTrees.size(); ++j) {
for (int k = 0; k < rightTrees.size(); ++k) {
TreeNode* root = new TreeNode(i);
root->left = leftTrees[j];
root->right = rightTrees[k];
result.push_back(root);
}
}
}
return result;
}
};