Unvisited
/* == the number of neighbors of square <r,c> that are unvisited. */
static int unvisited(int r, int c)
int count = 0; // # unvisited neighs.
for (int k = 0; k < 8; k++) {
int Nrow = r + deltaR[k];
int Ncol = c + deltaC[k];
if ( B[Nrow][Ncol] == Blank ) count++;