LeetCode 96 不同的二叉搜索树

图解找递推公式

const int N = 20;
class Solution {
public:
    int dp[N];
    int numTrees(int n) {
        dp[0] = 1;
        for (int i = 1; i <= n; i ++)
            for (int j = 0; j <= i - 1; j ++)
                dp[i] += dp[j] * dp[i - j - 1];

        return dp[n];
    }
};