[LeetCode] Pascal's Triangle

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]]

public class Solution {    public ArrayList<ArrayList<Integer>> generate(int numRows) {        ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();                for (int i = 0; i < numRows; i++) {            ArrayList<Integer> rowList = new ArrayList<Integer>();            // add an element            for (int j = 0; j <= i; j++) {                if (j == 0 || j == i) rowList.add(1);                else rowList.add(list.get(i-1).get(j-1) + list.get(i-1).get(j));            }                        // add a row            list.add(rowList);        }                return list;    }}