Leetcode#120 Triangle

 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 }