LeetCode OJ ：Unique Binary Search Trees II（唯一二叉搜尋樹）

標籤：

題目如下所示：返回的結果是一個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
　　
樹節點的定義是下面這樣的 

 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 };

這一題實際上更另外一個叫做different ways to add parentheses的題目比較相似，這個也是詳見博文

LeetCode OJ ：Unique Binary Search Trees II（唯一二叉搜尋樹）