C++ - Zadatak Kule (rješenje)

/*
    Zadatak: Kule
             http://bit.ly/zadatak-kule

    Složenost: << faktorijelna zbog memoizacije!

    Datum: 2013-03-01

    Autor: Goran Žužić, HSIN

    Ponuđeno rješenje: Kristijan Burnik, udruga informatičara Božo Težak

    Gmail: kristijanburnik
*/
#include <iostream>
#include <cstdlib>
#include <cmath>

using namespace std;

int n;
int a[20][20];
int sums[0x100000] = {0};

int maxsuma(int free,int size) {

   int saved = sums[free];
   if (saved > 0) return saved;

   if (size == 2) {
        int r[2] = {n-2,n-1};
        int c[2] = {0,0};
        int cc = 0;
        int bits = free;

        for (int i = 0; i < n && cc<2; i++) {
            if (bits & 1) {
                c[cc] = i;
                cc++;
            }
            bits >>= 1;
        }

        return (
            sums[free] = max (
                        a[ r[0] ][ c[0] ] + a[ r[1] ][ c[1] ] ,
                        a[ r[1] ][ c[0] ] + a[ r[0] ][ c[1] ]
                    )
        );
   }

   int r = n - size;
   int max = 0;
   int bits = free;
   int onecount = 0;

   for (int i = 0; i < n && onecount < size; i++) {
        if (bits & 1) {
            int suma = a[r][i] +  maxsuma(free - (1 << i), size - 1);
            if (suma > max) max = suma;
            onecount++;
        }
        bits >>= 1;
    }

    return sums[free] = max ;
}

int main(void) {

    cin >> n;
    for (int i = 0 ; i < n; i++)
        for (int j = 0 ; j < n; j++)
            cin >> a[i][j];

    int free = (1 << n) - 1;
    cout << maxsuma(free,n) << endl;

    return 0;
}