Triangle [LeetCode]

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.

Solution: 

class Solution {
public:
    int minimumTotal(vector<vector<int> > &triangle) {
        if(triangle.size() == 0)
            return 0;
        vector<int> totals;
        for(int i = 0; i < triangle.size(); i ++) {
            if(i == 0){
                totals.push_back(triangle[0][0]);
                continue;
            }
            vector<int> new_total;
            for(int j = 0; j < triangle[i].size(); j ++) {
                int sum = 0;
                if(j - 1 < 0)
                    sum = triangle[i][j] + totals[j];
                else if (j > totals.size() - 1)
                    sum = triangle[i][j] + totals[j - 1];
                else 
                    sum = min(triangle[i][j] + totals[j - 1], triangle[i][j] + totals[j]);
                    
                new_total.push_back(sum);
            }
            totals = new_total;
        }
        
        int min_total = totals[0];
        for(int i = 1; i < totals.size(); i ++) {
            if(totals[i] < min_total)
                min_total = totals[i];
        }
        return min_total;
    }
};