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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) {} * }; */ struct TreeNode { int val; TreeNode *left; TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) {} }; class Solution { public: std::vector<TreeNode *> generateTrees(int n) { return dfs(0,n-1); } private: std::vector<TreeNode *> dfs(int n, int m) { std::vector<TreeNode *> res; if(n > m) { res.push_back(NULL); return res; } for (int i = n; i <= m; i++) { std::vector<TreeNode *> left = dfs(n,i-1); std::vector<TreeNode *> right= dfs(i+1,m); for (int j = 0; j < left.size(); j++) { for (int k = 0; k < right.size(); k++) { TreeNode *node = new TreeNode(i+1); res.push_back(node); node->left = left[j]; node->right= right[k]; } } } return res; } };
leetcode - Unique Binary Search Trees II
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