class Solution {
public:
int numTrees(int n) {
vector
f[0] = 1;
f[1] = 1;
for (int i = 2; i <= n; ++i){
for (int k = 1; k <= i; ++k)
f[i] = f[i] + f[k - 1] * f[i - k];
}
return f[n];
}
};
2385
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