void block_groups(Sudoku &sudoku, int group_size, int row_block, int col_block)
{
HammingWeightIterator subset_iter(group_size);
int digit_subset;
// for each set of n numbers S = {k1, k2, ... kn}:
while ((digit_subset = subset_iter.next()) != -1)
{
// C(k) == set of columns containing k
// C(S) == union of C(k) over k in S
int blocks_containing = blockcells_containing_any(sudoku, row_block, col_block, digit_subset);
// if size(C(S)) == n
if (num_ones(blocks_containing) == group_size)
{
// remove all other possibilities from columns in C(S)
SetBitIndexIterator block_iter(blocks_containing);
auto end = SetBitIndexIterator::end();
for (; block_iter != end; ++block_iter)
{
int row, col;
blockunmask(mask(*block_iter), row, col);
row += row_block * 3;
col += col_block * 3;
int prev = sudoku(row, col);
sudoku.set(row, col, prev & digit_subset);
}
}
}
}
/* applies a client provided apply function to each element in the array2b
* in a block-major fashion.
*/
void UArray2b_map(T array2b, void apply(int i, int j, T array2b,
void *elem, void *cl), void *cl)
{
assert(array2b);
int row, col;
int w = array2b->width;
int h = array2b->height;
int bs = array2b->blocksize;
for (row = 0; row < block_dim(h, bs); row++){
for(col = 0; col < block_dim(w, bs); col++){
/* now iterate through each block */
block_iter(array2b, col, row, apply, cl);
}
}
}