Unique_Binary_Search_Trees.java

import java.util.Scanner;

/**
 * Created by xynophon on 15.1.27.
 */
public class Unique_Binary_Search_Trees {
    public int solution(int n){
        int dbnum = 2*n;
        long result = 1;
        int cnt = 0;
        while(dbnum > 0){
            cnt++;
            if(cnt < n)
                result *= dbnum--;
            else if (cnt == n)
                dbnum--;
            else
                result /= dbnum--;
        }
        return (int)result;
    }

    public static void main(String args[]){
        Unique_Binary_Search_Trees ubst = new Unique_Binary_Search_Trees();
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println(ubst.solution(n));
    }
}