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题目如下所示：返回的结果是一个Node的Vector：
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
树节点的定义是下面这样的
1 /** 2 * Definition for a binary tree node. 3 * struct TreeNode { 4 * int val; 5 * TreeNode *left; 6 * TreeNode *right; 7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8 * }; 9 */ 10 class Solution { 11 public: 12 vector<TreeNode*> generateTrees(int n) { 13 return createNode(1, n); 14 } 15 16 vector<TreeNode*> createNode(int start, int end) 17 { 18 vector<TreeNode*> result; 19 if(start > end){ 20 result.push_back(NULL); 21 return result; 22 } 23 for(int i = start; i <= end; ++i){ 24 vector<TreeNode*> leftNode = createNode(start, i - 1); 25 vector<TreeNode*> rightNode = createNode(i + 1, end); 26 for(int j = 0; j < leftNode.size(); ++j){ 27 for(int k = 0; k < rightNode.size(); ++k){ 28 TreeNode * tmpNode = new TreeNode(i); 29 tmpNode->left = leftNode[j]; 30 tmpNode->right = rightNode[k]; 31 result.push_back(tmpNode); 32 } 33 } 34 } 35 return result; 36 } 37 };
这一题实际上更另外一个叫做different ways to add parentheses的题目比较相似，这个也是详见博文
LeetCode OJ ：Unique Binary Search Trees II（唯一二叉搜索树）
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原文地址：http://www.cnblogs.com/-wang-cheng/p/4853982.html
