leetcode-95-树题-不同的二叉搜索树

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题目

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解法

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

// 递归，分别以每个数字为根节点，两边数字为左右子树，遍历
class Solution {
public:
    vector<TreeNode*> generateTrees(int n) {
        vector<TreeNode*> res;
        if(0 == n) return res;
        res = helper(1, n);
        return res;
    }

    vector<TreeNode*> helper(int start, int end){
        vector<TreeNode*> res;
        if(start > end) res.push_back(NULL);

        for(int i = start; i <= end; ++i){
            auto lefts = helper(start, i-1);
            auto rights = helper(i+1, end);
            for(auto l : lefts){
                for(auto r : rights){
                    TreeNode *root = new TreeNode(i);
                    root->left = l;
                    root->right = r;
                    res.push_back(root);
                }
            }
        }

        return res;
    }
};