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

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
void fill(TreeNode* &node, int &num)
{
if(node == NULL)return;
fill(node->left,num);
node->val = num;
num++;
fill(node->right,num);
return;
}

void copytree(TreeNode *src, TreeNode * &des)
{
if(src == NULL)return;
TreeNode *node = new TreeNode(0);
des = node;
copytree(src->right,des->right);
copytree(src->left,des->left);
return;
}

void create(vector<TreeNode*> &ret,int n)
{
vector<vector<TreeNode*> > v;
vector<TreeNode*> a;
vector<TreeNode*> b;
a.push_back(NULL);
TreeNode *fnode = new TreeNode(0);
b.push_back(fnode);
v.push_back(a);
v.push_back(b);

for(int i = 2; i <= n; i++)
{
vector<TreeNode*> c;
for(int j = 0; j < i; j++)
{
int k = v[j].size();
int m = v[i-1-j].size();
for(int l = 0; l < k; l++)
{
for(int r = 0; r < m; r++)
{
TreeNode *node = new TreeNode(0);
TreeNode *des = NULL;
copytree(v[j][l],des);
node->left = des;
des = NULL;
copytree(v[i-1-j][r],des);
node->right = des;
c.push_back(node);
}
}
}
v.push_back(c);
}

int length = v.size();
ret = v[length-1];
return;
}

vector<TreeNode *> generateTrees(int n) {
vector<TreeNode*> ret;

vector<TreeNode*> a;
a.push_back(NULL);
if(n == 0)return a;

create(ret,n);

int len = ret.size();
for(int i = 0; i < len; i++)
{
int num = 1;
fill(ret[i],num);
}

return ret;
}
};