004.cpp

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#include <iostream>
int
main ()
{
  unsigned max_product = 0;
  int a = 0, b = 0;
  for (int i = 999; i >= 100; i--)
    for (int j = 999; j >= 100; j--)
      if(i>=j){//Avoid symmetry
        unsigned product = i * j;

        if (product < max_product)
          continue;             //Exclude smaller products

        if (product >= 1e5)     //six digits
          {
            if (product / unsigned(1e5) == product % 10
                && product / unsigned(1e4) % 10 == product / 10 % 10
                && product / unsigned(1e3) % 10 == product / 100 % 10)
              {
                max_product = product;
                a = i;
                b = j;
              }
          }
        else                    //five digits
        if (product / unsigned(1e4) == product % 10
              && product / unsigned(1e3) % 10 == product / 10 % 10)
          {
            max_product = product;
            a = i;
            b = j;
          }
      }

std::cout << a << " * " << b << " = " << max_product << std::endl;
  return 0;
}