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.

实现：

class Solution {
public:
    int minimumTotal(vector<vector<int>>& triangle) {
        int n = triangle.size();
        for (int i=n-2; i >=0; i--) {
            for (int j = 0; j < triangle[i].size(); j++) {
                triangle[i][j] += triangle[i+1][j] < triangle[i+1][j+1] ? triangle[i+1][j] : triangle[i+1][j+1];
            } 
        }
        return triangle[0][0];
    }
};