96. 不同的二叉搜索树

class Solution {
public:
    int numTrees(int n) {
        if (n==0) {
            return 1;
        }
        vector<int> dp(n+1, 0);
        dp[0] = 1;
        dp[1] = 0;
        for (int i = 1; i <= n; i++) {
            for (int j = 0; j < i; j++) {
                dp[i] += dp[j] * dp[i - 1 - j];
            }
        }
        return dp[n];
    }
}; 
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