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