LeetCode "Unique Binary Search Trees II"

最新推荐文章于 2020-12-09 16:51:01 发布

转载最新推荐文章于 2020-12-09 16:51:01 发布 · 50 阅读

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原文链接：http://www.cnblogs.com/tonix/p/3879839.html

本文介绍了一种使用递归方法生成所有可能的唯一二叉搜索树的方法。通过递归地构造左子树和右子树，并组合它们来创建根节点的不同结构，实现了LeetCode上Unique Binary Search Trees II的问题解决方案。

I fell in a deadloop, and didn't see the actual recursion pattern.

Reference:http://fisherlei.blogspot.com/2013/03/leetcode-unique-binary-search-trees-ii.html

class Solution {
public:
    vector<TreeNode *> generate(int s, int e)
    {
        vector<TreeNode *> subTree; 
        if(s > e)    
        {
            subTree.push_back(NULL);
            return subTree;
        }

        for(int i = s; i <= e; i++)  
                {
            vector<TreeNode*> leftSubs = generate(s, i-1);  
            vector<TreeNode*> rightSubs = generate(i+1, e);  
            for(int j = 0; j < leftSubs.size(); j ++)
            for(int k = 0; k < rightSubs.size(); k ++)
            {
                TreeNode *pRoot = new TreeNode(i);
                pRoot->left = leftSubs[j];
                pRoot->right= rightSubs[k];
                subTree.push_back(pRoot);
            }
        }
        return subTree;
    }
    vector<TreeNode *> generateTrees(int n) {
        if(n == 0) return generate(1,0);
        return generate(1, n);
    }
};