December 2013 Bronze Problem 3: Wormholes

Result: incomplete

It's too difficult, but I had it partially done. Other partial work is in the recycling by now.

wormhole.cpp

#include <iostream>
#include <fstream>

#include <map>

#define loopi(x) loop_start(i,x,0)
#define loopj(x) loop_start(j,x,0)
#define loop_start(i, x,s) for(int i = (s); i < (x); ++i)
#define loop_rev(a,x,stop) for(int a = (x); a >= (stop); --a)

using namespace std;

// table for n! from 0! to 12!
const unsigned int factorial[] = {
 1,
 1,
 2,
 6,
 24,
 120,
 720,
 5040,
 40320,
 362880,
 3628800,
 39916800,
 479001600,
};

// table for 2^n from 2^0 to 2^6
const unsigned int pow2N[] = {
 1,
 2,
 4,
 8,
 16,
 32,
 64,
};

int pairings(int N){
 return factorial[N]/pow2N[N/2+1];
}

int main() {
 ofstream fout ("wormhole.out");
 ifstream fin ("wormhole.in");
 // Count number of wormholes per row
 int N;
 fin >> N;
 map<int, int> counts;
 loopi(N){
  int x, y;
  fin >> x >> y;
  ++counts[y];
 }
 int total = pairings(N);
 // Count the rows with one item
 int rows_with_one = 0;
 // Calculate the working combinations of the remaining...
 int remaining_combinations = 0;
 int working = remaining_combinations * pairings(rows_with_one);
 fout << (total - working) << endl;
 return 0;
}