118 Pascal's Triangle

public class Solution {
    public ArrayList<ArrayList<Integer>> generate(int numRows) {
        ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
        if (numRows == 0) {
            return res;
        }
        
        
        ArrayList<Integer> first = new ArrayList<Integer>();
        first.set(0, 1);
        res.add(first);
        
        for (int i = 1; i < numRows; i++) {
            ArrayList,
        }
    }
}