LeetCoder - Triangle

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.
For example, given the following triangle

[
     [2],
    [3,4],
   [6,5,7],
  [4,1,8,3]
]

The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).

Note:
Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.

public class Solution {
    public int minimumTotal(ArrayList<ArrayList<Integer>> triangle) {
        for(int i=triangle.size()-2;i>=0;i--) {
            for(int j=0;j<triangle.get(i).size();j++) {
                triangle.get(i).set(j, triangle.get(i).get(j) + (triangle.get(i+1).get(j)<triangle.get(i+1).get(j+1)?triangle.get(i+1).get(j):triangle.get(i+1).get(j+1)));
            }
        }
        return triangle.get(0).get(0);
    }
}