代码随想录：不同的二叉搜索树

class Solution {
public:
    int numTrees(int n) {
        vector<int> dp = vector<int>(n + 1, 0);
        dp[0] = 1;
        dp[1] = 1;
        for (int i = 2; i <= n; i++) {
            int sum = 0;
            for (int j = 1; j <= i; j++) {
                // 当j为根节点时，可能性有左侧子节点*右侧子节点
                sum += dp[j-1] * dp[i - j];
            }
            dp[i] = sum;
        }
        return dp[n];
    }
};