[leetcode] Unique Binary Search Trees II

Given n, generate all structurally unique BST's (binary search trees) that store values 1...n.

For example,

Given n = 3, your program should return all 5 unique BST's shown below.

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

思路：也是采用动态规划思路，只不过需要将函数改写一下；
代码：

/**
* Definition for binary tree
* 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) {
return generate(1,n);
}
vector<TreeNode *> generate(int start, int end){
vector<TreeNode *> res;
if(start>end){
res.push_back(NULL);
return res;
}
for(int i=start;i<=end;i++){
vector<TreeNode *> left,right;
left=generate(start,i-1);
right=generate(i+1,end);
int leftLen=left.size(),rightLen=right.size();
for(int ii=0;ii<leftLen;ii++){
for(int jj=0;jj<rightLen;jj++){
TreeNode *temp=new TreeNode(i);
temp->left=left[ii];
temp->right=right[jj];
res.push_back(temp);
}
}
}
return res;
}
};