LeetCode OJ:Unique Binary Search Trees II

Unique Binary Search Trees II

 

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.

算法思想：

DFS罗列所有可能情况：

/** * 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 *>result;        if(start>end){            result.push_back(NULL);            return result;        }        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 *root=new TreeNode(i);                    root->left=left[j];                    root->right=right[k];                    result.push_back(root);                }        }        return result;    }    vector<TreeNode *> generateTrees(int n) {        return generate(1,n);    }};