011.cpp

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#include <iostream>
#include <fstream>
using namespace std;

int
main ()
{
  ifstream input;
  input.open ("011.txt");

  unsigned short N[20][20];
  for (unsigned short *p = &(N[0][0]); !input.eof (); p++)
    input >> *p;

  unsigned max_product = 0;
  int x1, y1, x2, y2;

//Search in rows
  for (int i = 0; i < 20; i++)
    for (int j = 0; j < 20 - 3; j++)
      {
        unsigned product =
          unsigned (N[i][j]) * N[i][j + 1] * N[i][j + 2] * N[i][j + 3];
        if (product > max_product)
          {
            max_product = product;
            x1 = i;
            y1 = j;
            x1 = i;
            y2 = j + 3;
          }
      }

//Search in columns
  for (int j = 0; j < 20; j++)
    for (int i = 0; i < 20 - 3; i++)
      {

        unsigned product =
          unsigned (N[i][j]) * N[i + 1][j] * N[i + 2][j] * N[i + 3][j];

        if (product > max_product)
          {
            max_product = product;
            x1 = i;
            y1 = j;
            x2 = i + 3;
            y2 = j;
          }
      }

//Search from top-left to bottom-right
  for (int i = 0; i < 20 - 3; i++)
    for (int j = 0; j < 20 - 3; j++)
      {

        unsigned product =
          unsigned (N[i][j]) * N[i + 1][j + 1] * N[i + 2][j + 2] * N[i +
                                                                     3][j +
                                                                        3];

        if (product > max_product)
          {
            max_product = product;
            x1 = i;
            y1 = j;
            x2 = i + 3;
            y2 = j + 3;
          }
      }

//Search from top-right to bottom-left
  for (int i = 0; i < 20 - 3; i++)
    for (int j = 3; j < 20; j++)
      {

        unsigned product =
          unsigned (N[i][j]) * N[i + 1][j - 1] * N[i + 2][j - 2] * N[i +
                                                                     3][j -
                                                                        3];

        if (product > max_product)
          {
            max_product = product;
            x1 = i;
            y1 = j;
            x2 = i + 3;
            y2 = j - 3;
          }
      }
  cout << max_product << endl << " from row " << (x1 + 1) << ", column "
    << (y1 + 1) << " to row " << (x2 + 1) << ", column " << (y2 + 1) << endl;
  return 0;
}