LeetCode OJ ：Unique Binary Search Trees II（唯一二叉搜索树）

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

 /**

  * Definition for a binary tree node.

  * struct TreeNode {

  *     int val;

  *     TreeNode *left;

  *     TreeNode *right;

  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

  * };

  */

 class Solution {

 public:

     vector<TreeNode*> generateTrees(int n) {

         return createNode(, n);

     }

     vector<TreeNode*> createNode(int start, int end)

     {

         vector<TreeNode*> result;

         if(start > end){

             result.push_back(NULL);

             return result;

         }

         for(int i = start; i <= end; ++i){

             vector<TreeNode*> leftNode = createNode(start, i - );

             vector<TreeNode*> rightNode = createNode(i + , end);

             for(int j = ; j < leftNode.size(); ++j){

                 for(int k = ; k < rightNode.size(); ++k){

                     TreeNode * tmpNode = new TreeNode(i);

                     tmpNode->left = leftNode[j];　　

                     tmpNode->right = rightNode[k];

                     result.push_back(tmpNode);

                 }

             }

         }

         return result;

     }

 };

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，这个详见上一篇博文。

java版本的代码如下：

 /**

  * Definition for a binary tree node.

  * public class TreeNode {

  *     int val;

  *     TreeNode left;

  *     TreeNode right;

  *     TreeNode(int x) { val = x; }

  * }

  */

 public class Solution {

     public List<TreeNode> generateTrees(int n) {

         if(n == )//如果不加上这一条，当为0的时候会返回[[]]，不知道为什么，很奇怪

             return new ArrayList<TreeNode>();

         return createTree(, n);

     }

     public List<TreeNode> createTree(int start, int end){

         ArrayList<TreeNode> result = new ArrayList<TreeNode>();

         if(start > end){

             result.add(null);

             return result;

         }

         for(int i = start; i <= end; ++i){

             for(TreeNode leftNode : createTree(start, i - )){

                 for(TreeNode rightNode : createTree(i + , end)){

                     TreeNode node = new TreeNode(i);

                     node.left = leftNode;

                     node.right = rightNode;

                     result.add(node);

                 }

             }

         }

         return result;

     }

 }

巴特西

LeetCode OJ ：Unique Binary Search Trees II（唯一二叉搜索树）

最新文章

热门文章