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.

class Solution {
public:
    int minimumTotal(vector<vector<int> > &triangle) {
        int m=triangle.size();
        if(m==0)return 0;
        int n=triangle[0].size();
        if(n==0)return 0;
        vector<int> f=triangle[m-1];
        for(int i=m-2;i>=0;i--)
        {
            for(int j=0;j<i+1;j++)
            {
                f[j]=(f[j]<f[j+1]?f[j]:f[j+1])+triangle[i][j];
            }
        }
        return f[0];
    }
};