LeetCode OJ 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

confused what

"{1,#,2,3}"

means? >
read more on how binary tree is serialized on OJ.

https://leetcode.com/discuss/9790/java-solution-with-dp

偷偷改成了C++版本：

class Solution {
public:
	vector<TreeNode *> generateTrees(int n) {
		vector<vector<TreeNode *> > dp(n + 1);
		dp[0].push_back(NULL);
		for (int len = 1; len <= n; len++) {
			for (int j = 0; j < len; j++) {
				for (int k1 = 0; k1 < dp[j].size(); k1++) {
					for (int k2 = 0; k2 < dp[len - j - 1].size(); k2++) {
						TreeNode * nodeL = dp[j][k1];
						TreeNode * nodeR = dp[len - j - 1][k2];
						TreeNode * node = new TreeNode(j + 1);
						node->left = nodeL;
						node->right = clone(nodeR, j + 1);
						dp[len].push_back(node);
					}
				}
			}
		}
		return dp
;
	}
	TreeNode * clone(TreeNode * n, int offset) {
		if (!n) return NULL;
		TreeNode * node = new TreeNode(n->val + offset);
		node->left = clone(n->left, offset);
		node->right = clone(n->right, offset);
		return node;
	}
};