题目

unique-binary-search-trees-ii

2. 算法

• catalan数-卡塔兰数

3. 代码

class Solution {

public:

    int numTrees(int n) {

        vector<int> dp(n + 1, 0);

        dp[0] = 1;

        dp[1] = 1;

        for (int i = 2; i <= n; ++i) {

            for (int j = 0; j < i; ++j) {

                dp[i] += dp[j] * dp[i - j - 1];

            }

        }

        return dp[n];

    }

};