欧拉项目11

Question

我正在忙于项目欧拉,我正在努力解决问题11,但答案似乎是错误的.但我不明白为什么,代码似乎是正确的.

vector<vector<int> > grid;
    ifstream stream("/home/uauser/workspace/Project_euler/grid.txt");
    string line;
    char *tok;
    if (stream.is_open())
    {
        while(stream.good())
        {
            getline(stream, line);
            tok = strtok((char *)line.c_str(), " ");
            vector<int> row;
            while (tok != NULL)
            {
                int field;
                stringstream ss;
                ss << tok;
                ss >> field;
                row.push_back(field);

                tok = strtok(NULL, " ");
            }
            grid.push_back(row);
        }
        stream.close();
    }

    int product = 0;
    for(unsigned int i = 0; i < grid.size(); i++)
    {
        for(unsigned int j = 0; j < grid.at(i).size(); j++)
        {
            if( i < 17)
            {
                product = max(product, grid.at(i).at(j) * grid.at(i + 1).at(j) * grid.at(i + 2).at(j) * grid.at(i + 3).at(j));
            }
            if( j < 17)
            {
                product = max(product, grid.at(i).at(j) * grid.at(i).at(j+1)* grid.at(i).at(j+2) * grid.at(i).at(j + 3));
            }
            if((j < 17) && (i < 17) && (j >= 3) && (i >= 3))
            {
                product = max(product, grid.at(i).at(j) * grid.at(i-1).at(j+1) * grid.at(i-1).at(j+2) * grid.at(i -3).at(j+3));
                product = max(product, grid.at(i).at(j) * grid.at(i+1).at(j-1) * grid.at(i+1).at(j-2) * grid.at(i +3).at(j-3));
                product = max(product, grid.at(i).at(j) * grid.at(i+1).at(j+1) * grid.at(i+1).at(j+2) * grid.at(i + 3).at(j + 3));
                product = max(product, grid.at(i).at(j) * grid.at(i-1).at(j-1) * grid.at(i-1).at(j-2) * grid.at(i -3).at(j-3));
            }
            cout<<product<<endl;

        }
    }
    cout<<"The Product is: "<<product<<endl;
}

播下代码读取的txt文件没有问题,但是当他需要找到最大值时才得到错误的答案.

Answer 1

对角线的指数是错误的.例如:

... * grid.at(i-1).at(j+1) * grid.at(i-1).at(j+2) * grid.at(i -3).at(j+3))

中间部分应该i-2而不是i-1.与其他对角线类似的问题.