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) {// Start typing your Java solution below// DO NOT write main() functionArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();ArrayList<Integer> line;if(numRows < 1)return res;for(int i = 0; i < numRows; i++){line = new ArrayList<Integer>();for(int j = 0; j <= i; j++){if(j == 0)line.add(1);else if(j == i)line.add(1);elseline.add(res.get(i - 1).get(j - 1) + res.get(i - 1).get(j));}res.add(line);}return res;}}