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(List<List<Integer>> triangle) {
        int m=triangle.size();
        int []f=new int[m+1];
        for(int i=m-1;i>=0;i--){
            for(int j=0;j<=i;j++){
                f[j]=Math.min(f[j],f[j+1])+triangle.get(i).get(j);
            }
        }
        return f[0];
    }
}