#include <iostream>
#include <vector>

using std::cout;

inline bool validnet(const int &activators, const int &repressors)
{
   return (activators & repressors) == 0;
}

inline bool isfp(int activators, int repressors, int state)
{
   int ns = 0;
   for(int b = 0; b < 4; ++b)
   {
      int a = activators & 0xf;
      int r = repressors & 0xf;
      // Require that all regulated bits = 1
      // It matters not whether the unregulated genes are all 0 or all 1.
      if((state & a) == a && (~state & r) == r)
         ns |= 1 << b;
      activators >>= 4;
      repressors >>= 4;
   }
   return ns == state;
}

inline int fixedpoints(int activators, int repressors)
{
   int fps = 0;
   for(int state = 0; state < 16; ++state)
      if(isfp(activators, repressors, state))
         ++fps;
   return fps;
}

void printfphistogram()
{
   std::vector<int> fphistogram(17, 0);
   for(int act = 0; act < 0x10000; ++act)
      for(int rep = 0; rep < 0x10000; ++rep)
         if(validnet(act, rep))
            ++fphistogram[fixedpoints(act, rep)];

   cout << "#FPs\tcount\n";
   for(int i = 0; i < 17; ++i)
      cout << i << "\t" << fphistogram[i] << "\n";
}

int main()
{
   printfphistogram();
}

/*
Output:

#FPs    count
0       13109930
1       19907908
2       7666109
3       1811682
4       426406
5       92895
6       24358
7       5033
8       1830
9       335
10      204
11      0
12      30
13      0
14      0
15      0
16      1


*/