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.

class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        int n = triangle.size();
        if (n == 0)
            return 0;
        List<Integer> last = triangle.get(n - 1);
        for (int i = n - 2; i >= 0; i--) {
            // Not destroying the rows of triangle
            List<Integer> temp = new ArrayList<>(triangle.get(i));
            for (int j = 0; j < temp.size(); j++)
                // As seen from structure the adjacent elements are j and j+1
                temp.set(j, temp.get(j) + Math.min(last.get(j), last.get(j + 1)));
            last = temp;
        }
        return last.get(0);
    }
}