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[LeetCode] Unique Binary Search Trees II （难以忍受的递归）
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
class Solution {private: vector<TreeNode*> generateTreesRec(int start, int end){ vector<TreeNode*> v; if(start > end){ v.push_back(NULL); return v; } for(int i = start; i <= end; ++i){ vector<TreeNode*> left = generateTreesRec(start, i - 1); vector<TreeNode*> right = generateTreesRec(i + 1, end); TreeNode *node; for(int j = 0; j < left.size(); ++j){ for(int k = 0; k < right.size(); ++k){ node = new TreeNode(i); node->left = left[j]; node->right = right[k]; v.push_back(node); } } } return v; }public: vector<TreeNode *> generateTrees(int n) { return generateTreesRec(1, n); }};
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