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:

 1 class Solution {
 2 public:
 3     int minimumTotal(vector<vector<int> > &triangle) {
 4         if(triangle.size() == 0)
 5             return 0;
 6         vector<int> totals;
 7         for(int i = 0; i < triangle.size(); i ++) {
 8             if(i == 0){
 9                 totals.push_back(triangle[0][0]);
10                 continue;
11             }
12             vector<int> new_total;
13             for(int j = 0; j < triangle[i].size(); j ++) {
14                 int sum = 0;
15                 if(j - 1 < 0)
16                     sum = triangle[i][j] + totals[j];
17                 else if (j > totals.size() - 1)
18                     sum = triangle[i][j] + totals[j - 1];
19                 else 
20                     sum = min(triangle[i][j] + totals[j - 1], triangle[i][j] + totals[j]);
21                     
22                 new_total.push_back(sum);
23             }
24             totals = new_total;
25         }
26         
27         int min_total = totals[0];
28         for(int i = 1; i < totals.size(); i ++) {
29             if(totals[i] < min_total)
30                 min_total = totals[i];
31         }
32         return min_total;
33     }
34 };