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(vector<vector<int>>& triangle) {
        int n=triangle.size();
        if (n==0) {
            return 0;
        }
        else if (n==1) {
            return triangle[0][0];
        }
        else{
            for (int i = n-2; i>=0;--i)
            {
                for (int j=0; j<=i; j++) {
                    triangle[i][j]+=min(triangle[i+1][j],triangle[i+1][j+1]);
                }
            }
            return triangle[0][0];
        }
    }
};