1 int minimumTotal(vector<vector<int> > &triangle) { 2         if (triangle.empty()) return -1; 3          4         vector<int> layer(triangle[triangle.size() - 1]); 5          6         for (int i = triangle.size() - 2; i >= 0; i--) { 7             vector<int> upperLayer; 8             for (int j = 0; j <= i; j++) 9                 upperLayer.push_back(triangle[i][j] + min(layer[j], layer[j + 1]));10             layer = upperLayer;11         }12         13         return layer[0];14 }