[leetcode 95] Unique Binary Search Trees II

最新推荐文章于 2025-09-13 14:08:34 发布

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此博客介绍了如何生成所有结构独特的N个元素的二叉搜索树，包括实例演示和代码实现。

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

/**
 * 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 *> generateTrees(int n) {
       if (n == 0) {
           return dp(1,0);
       }
       return dp(1,n);
    }
    vector<TreeNode *> dp(int start, int end) {
        vector<TreeNode *> subTree;
        if (start > end) {
            subTree.push_back(NULL);
        }
        for (int k = start; k <= end; k++) {
            vector<TreeNode *> leftSub = dp(start, k-1);
            vector<TreeNode *> rightSub = dp(k+1, end);
            for (auto i:leftSub) {
                for (auto j:rightSub) {
                    TreeNode *root = new TreeNode(k);
                    root->left = i;
                    root->right = j;
                    subTree.push_back(root);
                }
            }
        }
        return subTree;
    }
};