|
(C)
#include <stdio.h> // GCC -O3 // a(7) in ~1.5 hours
char grid[8][8];
long long SIZE;
long long calc_ways(long long x, long long y) {
if (grid[x][y]) return 0;
grid[x][y] = 1;
long long n = calc_ways( x==0? SIZE-1 : x-1, y); // try West
if (SIZE>2)
n+= calc_ways( x==SIZE-1? 0 : x+1, y); // East
if (y>0) n+= calc_ways(x, y-1); // North
if (y==SIZE-1) n++;
else n+= calc_ways(x, y+1); // South
grid[x][y] = 0;
return n;
}
int main(int argc, char **argv)
{
for (SIZE=1; SIZE<7; ++SIZE) {
memset(grid, 0, sizeof(grid));
printf("%llu, ", calc_ways(0, 0)*SIZE);
}
printf("\n ");
for (SIZE=3; SIZE<9; ++SIZE) {
unsigned long long r;
memset(grid, 0, sizeof(grid));
grid[0][0]=1;
grid[0][1]=1;
r = calc_ways(0, 2)*SIZE; if (SIZE>6) printf(".");
r += calc_ways(1, 1)*SIZE*2; if (SIZE>6) printf(".");
grid[0][1]=0;
grid[1][0]=1;
r += calc_ways(1, 1)*SIZE*2; if (SIZE>6) printf(".");
r += calc_ways(2, 0)*SIZE*2; printf("%llu, ", r);
}
}
| 