Shortest solution using dp


#1

int Solution::numTrees(int n) {
int dp[n+1];
dp[0]=1;
dp[1]=1;
for(int i=2;i<=n;i++)
{
dp[i]=0;
for(int j=0;j<i;j++)
dp[i]+=dp[j]*dp[i-1-j];
}
return dp[n];
}