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 List<List<Integer>> generate(int numRows) {
        List<List<Integer> > pascalTriangle = new ArrayList<List<Integer> >();
        List<Integer> row1 = new ArrayList<Integer>();
        row1.add(1);
        List<Integer> row2 = new ArrayList<Integer>();
        row2.add(1); 
        row2.add(1);
		if(numRows == 1)
			pascalTriangle.add(row1);
		if(numRows == 2){
			pascalTriangle.add(row1);
			pascalTriangle.add(row2);
		}
		if(numRows > 2){
            pascalTriangle.add(row1);
			pascalTriangle.add(row2);
		    for(int i = 3; i <= numRows; ++i){
			    List<Integer> upList = pascalTriangle.get(i - 2);
			    List<Integer> currentList = new ArrayList<Integer>();
			    currentList.add(1);
			    for(int j = 1; j < i - 1; ++j)
				    currentList.add(upList.get(j - 1) + upList.get(j));
			    currentList.add(1);
			    pascalTriangle.add(currentList);
		    }
		}
		return pascalTriangle;    
    }
}