Optimizing Code - need some guidance

I recently tried my hand at CodeSprint2 through Interview Street. Having not coded in quite some time, I wasn't surprised that I had difficulty writing optimized code, but on one problem in particular I can't find where I've gone wrong. I've compared my code to successful alogrithms used by other programmers, and I don't see much difference. I tried in both Java and Ruby and hit a wall at the 4th test case with both (just learning Ruby so thought it would be a fun exercise to try it - I tweaked my algorithm a little in the process). Any recommendations would be appreciated, as this is driving me crazy.

The problem is Picking Cards and the description is here

Code in Java:

import java.io.*;
import java.util.*;
import java.math.*;

public class Cards3 {

    public Cards3()
    {
    }

     public void run()
    {
        ArrayList<Integer> cards = new ArrayList<Integer>();
        try{
            /*
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            String input = reader.readLine();

            StringTokenizer tokenizer = new StringTokenizer(input);
            int T = Integer.parseInt(tokenizer.nextToken());
            */

            DataInputStream reader = new DataInputStream(System.in);
            int T = reader.readInt();
            reader.readChar();
            System.out.println("T = " + T);
            //read in and test each subsequence
            for(int i = 0; i<T; i++)
            {
                /*
                input = reader.readLine();
                tokenizer = new StringTokenizer(input);
                int N = Integer.parseInt(tokenizer.nextToken());

                //read in and store cards
                String nextLine = reader.readLine();
                tokenizer = new StringTokenizer(nextLine);
                */

                int N = reader.readInt();
                reader.readChar();

                for(int j=0; j<N; j++)
                {
                    int next = reader.readInt();//Integer.parseInt(tokenizer.nextToken());
                    reader.readChar();
                    cards.add(next);
                }
                Collections.sort(cards);
                System.out.println(numWays(cards) % 1000000007);
                cards = new ArrayList<Integer>();
            }

            reader.close();
        }
        catch (IOException e)
        {
            System.out.println("Can not read input.");
        }
    }

    //computers the number of ways to pick up cards in currCards given that
    //numPicked cards have already been picked up
    public long numWays(ArrayList<Integer> cardsLeft)
    {
        int numPicked = 0;
        long numWays = 1;

        //calculate until all cards are picked up
        while(cardsLeft.size() >= 1)
        {
            //if we can't pick up the next card, we're at a dead end - no solutions
            if(cardsLeft.get(0) > numPicked)
                return 0;

            int numCanPick = 0;

            for(int i: cardsLeft)
            {   
                if(i <= numPicked)
                {
                    numCanPick++;

                }
                else
                {
                    break;
                }
            }

            cardsLeft.remove(0);
            numWays *= numCanPick;
            numWays = numWays % 1000000007;
            numPicked++;
        }

        return numWays;
    }

     public static void main(String args[])
       {
            Cards3 d = new Cards3();
            d.run();
       }
}

Code in Ruby

def runProgram
  answers = []
  t = STDIN.gets.to_i
  t.times{ 
    n = STDIN.gets
    numWays = 1
    cards = STDIN.gets.split.map(&:to_i)
    numPicked = 0
    for i in 0...cards.length
      numCanPick = cards.count{|a| a<= i}
      numWays = numWays * (numCanPick-i)
      break if numCanPick==0
      numWays = numWays % 1000000007
    end
     answers << numWays
  }

  puts answers
end

if __FILE__ == $0
 runProgram
 end

Thanks!