My code

… was written in C++ and can be compiled with G++, Clang++, Visual C++. You can download it, too. Or just jump to my GitHub repository.

       
#include <iostream>
       
#include <vector>
       
#include <cmath>
       
 
       
int main()
       
{
       
  // precompute all pairs a<b<c where a+b+c <= 3000
       
  const int MaxPerimeter = 3000;
       
  // -1 means "no triplets" for that perimeter
       
  const int NoSolution   =   -1;
       
 
       
  // cache[0] remains unused
       
  std::vector<int> cache(MaxPerimeter + 1, NoSolution);
       
 
       
  // scan all pairs a<b
       
  for (int a = 1; a < MaxPerimeter; a++)
       
    for (int b = a + 1; b < MaxPerimeter - a; b++)
       
    {
       
      // find c
       
      int c2 = a*a + b*b;
       
      // approximate square root as integer
       
      int c = sqrt(c2);
       
      // was it the correct square root ?
       
      if (c*c != c2)
       
        continue;
       
 
       
      // check summing condition
       
      int sum = a + b + c;
       
      if (sum > MaxPerimeter)
       
        break;
       
 
       
      // better solution than before ?
       
      if (cache[sum] < a*b*c)
       
        cache[sum] = a*b*c;
       
    }
       
 
       
  unsigned int tests;
       
  std::cin >> tests;
       
  while (tests--)
       
  {
       
    unsigned int n;
       
    std::cin >> n;
       
    // just lookup results (-1 if no solution)
       
    std::cout << cache[n] << std::endl;
       
  }
       
  return 0;
       
}

This solution contains 6 empty lines, 10 comments and 3 preprocessor commands.