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UniqueBinarySearchTreesII.cpp
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UniqueBinarySearchTreesII.cpp
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#include <vector>
using namespace std;
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
class Solution {
public:
/* Sol 0
* DP solution. O(n^4) time complexity.
* for n, choose i (1<=i<=n) as the root respectively.
*/
vector<TreeNode*> generateTrees(int n) {
vector<TreeNode*> result;
vector<vector<TreeNode*>> dp(n+1);
dp[0].push_back(nullptr);
if(n == 0) return result;
dp[1].push_back(new TreeNode(1));
for(int i = 2;i <= n;++i){
for(int j = 1;j <= i;++j){
for(int k1 = 0;k1 < dp[j-1].size();++k1){
for(int k2 = 0;k2 < dp[i-j].size();++k2){
TreeNode *temp = new TreeNode(j);
temp->left = dp[j-1][k1];
temp->right = addValue(dp[i-j][k2],i-j);
dp[i].push_back(temp);
}
}
}
}
return dp[n];
}
TreeNode* addValue(TreeNode *root,int val){
if(root == nullptr) return nullptr;
TreeNode *newRoot = new TreeNode(root->val + val);
newRoot->left = addValue(root->left,val);
newRoot->right = addValue(root->right,val);
return newRoot;
}
};