Leetcode 118 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]
]

Solution 1: simple looping

 public class Solution {  
   public List<List<Integer>> generate(int numRows) {  
     List<List<Integer>> res=new ArrayList<>();  
     for (int i=0; i<numRows; i++) {  
       List<Integer> one=new ArrayList<>();  
       for (int j=0; j<=i; j++) {  
         if (j==0 || j==i) one.add(1);  
         else one.add(res.get(i-1).get(j-1)+res.get(i-1).get(j));  
       }  
       res.add(one);  
     }  
     return res;  
   }  
 }