[leetcode] Unique Binary Search Trees II-优快云博客

本文链接：https://blog.youkuaiyun.com/mungco/article/details/10052315

本博客详细阐述了如何生成所有结构独特的二叉搜索树，覆盖从基本概念到具体实现的全过程。

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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.

这道题目在上一题的基础上需要我们把所有的树都输出！并且输出的格式需要按照leetcode的样子

class Solution {
public:
	vector<TreeNode *> generateTrees(int n) {
		// Start typing your C/C++ solution below
		// DO NOT write int main() function
		return generate(0,n-1);
	}
	vector<TreeNode*> generate(int begin,int end){
		vector<TreeNode* > ret;
		if(begin>end){
			ret.push_back(NULL);
			return ret;
		}
		for(int i=begin ; i<=end ; i++){
			vector<TreeNode* >leftTree=generate(begin,i-1);//all possible left trees
			vector<TreeNode* >rightTree=generate(i+1,end);//all possible right trees
			for(int j=0 ; j<leftTree.size() ; j++)
				for(int k=0 ; k<rightTree.size() ; k++){//all posiible trees with root i,left j,right k
					TreeNode *node=new TreeNode(i+1);
					ret.push_back(node);
					node->left=leftTree[j];
					node->right=rightTree[k];
				}
		}
		return ret;
	}
};