Pascal's Triangle

public class Solution {
    public ArrayList<ArrayList<Integer>> generate(int numRows) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if(numRows == 0) return result;
        ArrayList<Integer> first = new ArrayList<Integer>();
        first.add(1);
        result.add(first);
        for(int i=1; i<numRows; i++)
        {
            ArrayList<Integer> last = result.get(i-1);
            ArrayList<Integer> current = new ArrayList<Integer>();
            current.add(1);
            for(int j=1; j<i; j++)
            {
                current.add(last.get(j-1)+last.get(j));
            }
            current.add(1);
            result.add(current);
        }
        return result;
    }
}