[LeetCode 118] Pascal's Triangle

Question

link

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]
]

Stats

Frequency	1
Difficulty	2
Adjusted Difficulty
Time to use	--------

Ratings/Color = 1(white) 2(lime) 3(yellow) 4/5(red)

Analysis

This is a math question.

Below is my code.

Code

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