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.
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 a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: void generate(vector<TreeNode*> &res, int num, int offset) { if(0 == num) { res.push_back(NULL); return; } if(1 == num) { TreeNode* node = new TreeNode(num+offset); res.push_back(node); return; } for(int i=1;i<=num;i++) { vector<TreeNode*> left, right; generate(left, i - 1, offset); generate(right, num - i, offset + i ); for(int j=0;j<left.size();j++) { for(int k=0;k<right.size();k++) { TreeNode *cur = new TreeNode(i+offset); cur->left = left[j]; cur->right = right[k]; res.push_back(cur); } } } } vector<TreeNode*> generateTrees(int n) { vector<TreeNode*> res; generate(res, n, 0); return res; } };