Triangle

class Solution {
public:
    int minimumTotal(vector<vector<int>>& triangle) {
     int sum=0;
     if(triangle.size() == 0) return sum;
     sum = triangle[0][0];
     if(triangle.size() == 1) return sum;
     for(int i=triangle.size()-2;i>=0;i--){    //从倒数第二行开始，往前倒着算，看该结点从后min值
         for(int j=0;j<triangle[i].size();j++)
         {
             triangle[i][j]+=min(triangle[i+1][j],triangle[i+1][j+1]);
         }
     }
     return triangle[0][0];
    }
    
    
   /*
     递归的算法，这种会超时
     int getsum(vector<vector<int>>& triangle,int row,int pre_idx,int pre_sum){
        int sum1=pre_sum+triangle[row][pre_idx];
        int sum2=pre_sum+triangle[row][pre_idx+1];
        if(row == triangle.size()-1) return min(sum1,sum2);;
        int left=getsum(triangle,row+1,pre_idx,sum1);
        int right=getsum(triangle,row+1,pre_idx+1,sum2);
        return min(left,right);
    }*/
    
};