Project Euler Problem 11 - https://projecteuler.net/problem=11

problem11.cpp

#include <iostream>
#include <iomanip>

int grid[20][20] = {
    { 8, 2, 22, 97, 38, 15, 0, 40, 0, 75, 4, 5, 7, 78, 52, 12, 50, 77, 91, 8 },
    { 49, 49, 99, 40, 17, 81, 18, 57, 60, 87, 17, 40, 98, 43, 69, 48, 4, 56, 62, 0 },
    { 81, 49, 31, 73, 55, 79, 14, 29, 93, 71, 40, 67, 53, 88, 30, 3, 49, 13, 36, 65 },
    { 52, 70, 95, 23, 4, 60, 11, 42, 69, 24, 68, 56, 1, 32, 56, 71, 37, 2, 36, 91 },
    { 22, 31, 16, 71, 51, 67, 63, 89, 41, 92, 36, 54, 22, 40, 40, 28, 66, 33, 13, 80 },
    { 24, 47, 32, 60, 99, 3, 45, 2, 44, 75, 33, 53, 78, 36, 84, 20, 35, 17, 12, 50 },
    { 32, 98, 81, 28, 64, 23, 67, 10, 26, 38, 40, 67, 59, 54, 70, 66, 18, 38, 64, 70 },
    { 67, 26, 20, 68, 2, 62, 12, 20, 95, 63, 94, 39, 63, 8, 40, 91, 66, 49, 94, 21 },
    { 24, 55, 58, 5, 66, 73, 99, 26, 97, 17, 78, 78, 96, 83, 14, 88, 34, 89, 63, 72 },
    { 21, 36, 23, 9, 75, 0, 76, 44, 20, 45, 35, 14, 0, 61, 33, 97, 34, 31, 33, 95 },
    { 78, 17, 53, 28, 22, 75, 31, 67, 15, 94, 3, 80, 4, 62, 16, 14, 9, 53, 56, 92 },
    { 16, 39, 5, 42, 96, 35, 31, 47, 55, 58, 88, 24, 0, 17, 54, 24, 36, 29, 85, 57 },
    { 86, 56, 0, 48, 35, 71, 89, 7, 5, 44, 44, 37, 44, 60, 21, 58, 51, 54, 17, 58 },
    { 19, 80, 81, 68, 5, 94, 47, 69, 28, 73, 92, 13, 86, 52, 17, 77, 4, 89, 55, 40 },
    { 4, 52, 8, 83, 97, 35, 99, 16, 7, 97, 57, 32, 16, 26, 26, 79, 33, 27, 98, 66 },
    { 88, 36, 68, 87, 57, 62, 20, 72, 3, 46, 33, 67, 46, 55, 12, 32, 63, 93, 53, 69 },
    { 4, 42, 16, 73, 38, 25, 39, 11, 24, 94, 72, 18, 8, 46, 29, 32, 40, 62, 76, 36 },
    { 20, 69, 36, 41, 72, 30, 23, 88, 34, 62, 99, 69, 82, 67, 59, 85, 74, 4, 36, 16 },
    { 20, 73, 35, 29, 78, 31, 90, 1, 74, 31, 49, 71, 48, 86, 81, 16, 23, 57, 5, 54 },
    { 1, 70, 54, 71, 83, 51, 54, 69, 16, 92, 33, 48, 61, 43, 52, 1, 89, 19, 67, 48 }
};

long max_product = 0;

void calc_max(int x, int y);
void calc_horiz(int x, int y);
void calc_vert(int x, int y);
void calc_diag(int x, int y);

void calc_max_inv(int x, int y);
void calc_horiz_inv(int x, int y);
void calc_vert_inv(int x, int y);
void calc_diag_inv(int x, int y);


int main()
{
    for (int y = 0; y < 20; ++y)
        for (int x = 0; x < 20; ++x)
        {
            //std::cout << std::setw(2) << grid[x][y] << " ";
            //if (x == 19) std::cout << std::endl;
            if (y<16 && x<16)
                calc_max(x, y);
            else
                calc_max_inv(x, y);
        }
    std::cout << max_product << std::endl;
    return 0;
}


void calc_max(int x, int y)
{
    calc_horiz(x, y);
    calc_vert(x, y);
    calc_diag(x, y);
}

void calc_horiz(int x, int y)
{
    long prod = grid[x][y] * grid[x+1][y] * grid[x+2][y] * grid[x+3][y];
    if (prod > max_product)
        max_product = prod;
    /*
    std::cout << "Calculating horizontal product of " <<
        grid[x][y] << " " <<
        grid[x+1][y] << " " <<
        grid[x+2][y] << " " <<
        grid[x+3][y] << std::endl;
    */
}

void calc_vert(int x, int y)
{
    long prod = grid[x][y] * grid[x][y+1] * grid[x][y+2] * grid[x][y+3];
    if (prod > max_product)
        max_product = prod;
    /*
    std::cout << "Calculating vertical product of " <<
        grid[x][y] << " " <<
        grid[x][y+1] << " " <<
        grid[x][y+2] << " " <<
        grid[x][y+3] << std::endl;
    */       
}

void calc_diag(int x, int y)
{
    long prod = grid[x][y] * grid[x+1][y+1] * grid[x+2][y+2] * grid[x+3][y+3];
    if (prod > max_product)
        max_product = prod;
    // INVERTED DIAGONAL
    if (x-3>=0)
    {
        prod = grid[x][y] * grid[x-1][y+1] * grid[x-2][y+2] * grid[x-3][y+3];
        if (prod > max_product)
            max_product = prod;
    }
}

void calc_max_inv(int x, int y)
{
    calc_horiz_inv(x, y);
    calc_vert_inv(x, y);
    calc_diag_inv(x, y);    
}

void calc_horiz_inv(int x, int y)
{
    long prod = grid[x][y] * grid[x-1][y] * grid[x-2][y] * grid[x-3][y];
    if (prod > max_product)
        max_product = prod;
}

void calc_vert_inv(int x, int y)
{
    long prod = grid[x][y] * grid[x][y-1] * grid[x][y-2] * grid[x][y-3];
    if (prod > max_product)
        max_product = prod;
}

void calc_diag_inv(int x, int y)
{
    long prod = grid[x][y] * grid[x-1][y-1] * grid[x-2][y-2] * grid[x-3][y-3];
    if (prod > max_product)
        max_product = prod;
    // INVERTED DIAGONAL
    if (x+3<=19)
    {
        prod = grid[x][y] * grid[x+1][y-1] * grid[x+2][y-2] * grid[x+3][y-3];
        if (prod > max_product)
            max_product = prod;
    }

}