[leetcode]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.

动归不解释。

class Solution {
public:
    int minimumTotal(vector<vector<int> > &triangle) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int len = triangle.size();
        int *a;
        a = new int[len];
        a[0] = 0;
        int i,j;
        for(i = 0; i < len;i++)
        {
            
            for(j = i;j >= 0;j--)
            {
                if(j == 0)
                    a[j] = triangle.at(i).at(j) + a[j];
                else if(j == i)
                    a[j] = triangle.at(i).at(j) + a[j - 1];
                else
                {
                    int k = triangle.at(i).at(j);
                    k += (a[j]>a[j-1])?a[j-1]:a[j];
                    a[j] = k;
                }
            }
        }
        int min = 9999999;
        for(int i = 0; i <len;i++)
            min = (min > a[i])?a[i]:min;
        return min;
    }
};