LeetCode 95. Unique Binary Search Trees II

最新推荐文章于 2022-01-13 04:43:51 发布

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本文介绍了使用递归方法生成二叉树的过程，通过不断分解问题来构建完整的二叉树结构。

/**
 * 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 {
private:
    vector<TreeNode*> generateTrees(int beg, int end) {
        vector<TreeNode*> ret;
        if(beg > end) {
            ret.push_back(NULL);
            return ret;
        }
        for(int i = beg; i <= end; ++i) {
            vector<TreeNode*> leftTree = generateTrees(beg, i - 1);
            vector<TreeNode*> rightTree = generateTrees(i + 1, end);
            for(int j = 0; j < leftTree.size(); ++j) {
                for(int k = 0; k < rightTree.size(); ++k) {
                    TreeNode* node = new TreeNode(i  + 1);
                    ret.push_back(node);
                    node->left = leftTree[j];
                    node->right = rightTree[k];
                }
            }
        }
        return ret;
    }
public:
    vector<TreeNode*> generateTrees(int n) {
        vector<TreeNode*> result;
        if(n == 0) return result;
        return generateTrees(0, n - 1);
    }
};