120 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.

 

class Solution {
public:
    int minimumTotal(vector<vector<int> > &triangle) {
        if (triangle.empty()) return 0;
       
		int rows = triangle.size();
		vector<int> res = triangle[rows-1];
		for(int i = rows - 2;i >= 0;--i)
		{
			for(int j = 0;j < triangle[i].size();++j)
			{
				res[j] = min(res[j],res[j+1]) + triangle[i][j];
			}
		}

		return res[0];     
    }
};