原地旋转二维矩形阵列

http://en.wikipedia.org/wiki/In-place_matrix_transposition

x' = x cos f - y sin f
y' = y cos f + x sin f

x' = -y
y' =  x

// this function rotates 90 degrees
point successor(const point &p)
{
  return (-p.y, p.x);
}

// this function rotates 90 degrees in opposite direction
point predecessor(const point &p)
{
  return (p.y, -p.x);
}

void replace_cycle(const point &start)
{
  int data = get_data(start);
  point x = predecessor(start);
  while(x != start)
  {
    set_data(successor(x), get_data(x));
    x = predecessor(x);
  }
  set_data(successor(start), data);
}

void rotate_in_place()
{
  list<point> l;
  find_cycles(l);
  foreach(c in l)
  {
    replace_cycle(c);
  }
}

// Switch a and b
int a;
int b;
a ^= b;
b ^= a;
a ^= b;

for