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]

]

 

 1 public class Solution {

 2     public ArrayList<ArrayList<Integer>> generate(int numRows) {

 3         ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();

 4         List<Integer> item;

 5         if (numRows <= 0) return result;

 6         for (int i=0; i<numRows; i++) {

 7             item = new ArrayList<Integer>();

 8             for (int j=0; j<=i; j++) {

 9                 if (j==0 || j==i) item.add(1);

10                 else {

11                     List<Integer> prev = result.get(i-1);

12                     item.add(prev.get(j-1) + prev.get(j));

13                 }

14             }

15             result.add(new ArrayList<Integer>(item));

16         }

17         return result;

18     }

19 }