leetcode 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.

很明显的动态规划，当前总值只和上面的左右有关系，一次遍历就搞定

class Solution {
public:
    int minimumTotal(vector<vector<int>>& tri) 
    {
        for(int i=1;i<tri.size();i++) 
        {
            tri[i][0] += tri[i-1][0];
            tri[i][i] += tri[i-1][i-1];
            
            for (int j = 1; j < i; j++)
                tri[i][j] += min(tri[i-1][j-1], tri[i-1][j]);
        }
       
        return *min_element(tri[tri.size() - 1].begin(), tri[tri.size() - 1].end());
    }
};