Pascal's Triangle

Q:

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,
Return

[     [1],    [1,1],   [1,2,1],  [1,3,3,1], [1,4,6,4,1]]

Solution:

public class Solution {    public List<List<Integer>> generate(int numRows) {        List<List<Integer>> ret = new ArrayList<List<Integer>>();        if (numRows == 0)            return ret;        List<Integer> first = new ArrayList<Integer>();        first.add(1);        ret.add(first);        for (int i = 1; i < numRows; i++) {            List<Integer> prev = ret.get(i-1);            List<Integer> newlist = new ArrayList<Integer>();            newlist.add(1);            for (int j = 1; j < i; j++) {                int element = prev.get(j-1) + prev.get(j);                newlist.add(element);            }            newlist.add(1);            ret.add(newlist);        }        return ret;    }}