Unique Binary Search Trees

class Solution {

public:
int numTrees(int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
vector<int> f(n+2,0);
f[0]=1;
f[1]=1;
for(int i=2;i<=n;++i){
for(int j=1;j<=i;++j){
f[i]+=f[j-1]*f[i-j];
}
}
return f
;

}
};