#include "mincov_int.h"


static void
copy_row(register sm_matrix *A, register sm_row *prow)
{
    register sm_element *p;

    for(p = prow->first_col; p != 0; p = p->next_col) {
	(void) sm_insert(A, p->row_num, p->col_num);
    }
}

static int visit_row(sm_matrix *A, sm_row *prow, int *rows_visited, int *cols_visited);

static int
visit_col(sm_matrix *A, sm_col *pcol, int *rows_visited, int *cols_visited)
{
    sm_element *p;
    sm_row *prow;

    if (! pcol->flag) {
	pcol->flag = 1;
	(*cols_visited)++;
	if (*cols_visited == A->ncols) {
	    return 1;
	}
	for(p = pcol->first_row; p != 0; p = p->next_row) {
	    prow = sm_get_row(A, p->row_num);
	    if (! prow->flag) {
		if (visit_row(A, prow, rows_visited, cols_visited)) {
		    return 1;
		}
	    }
	}
    }
    return 0;
}

static int
visit_row(sm_matrix *A, sm_row *prow, int *rows_visited, int *cols_visited)
{
    sm_element *p;
    sm_col *pcol;

    if (! prow->flag) {
	prow->flag = 1;
	(*rows_visited)++;
	if (*rows_visited == A->nrows) {
	    return 1;
	}
	for(p = prow->first_col; p != 0; p = p->next_col) {
	    pcol = sm_get_col(A, p->col_num);
	    if (! pcol->flag) {
		if (visit_col(A, pcol, rows_visited, cols_visited)) {
		    return 1;
		}
	    }
	}
    }
    return 0;
}



int
sm_block_partition(sm_matrix *A, sm_matrix **L, sm_matrix **R)
{
    int cols_visited, rows_visited;
    register sm_row *prow;
    register sm_col *pcol;

    /* Avoid the trivial case */
    if (A->nrows == 0) {
	return 0;
    }

    /* Reset the visited flags for each row and column */
    for(prow = A->first_row; prow != 0; prow = prow->next_row) {
	prow->flag = 0;
    }
    for(pcol = A->first_col; pcol != 0; pcol = pcol->next_col) {
	pcol->flag = 0;
    }

    cols_visited = rows_visited = 0;
    if (visit_row(A, A->first_row, &rows_visited, &cols_visited)) {
	/* we found all of the rows */
	return 0;
    } else {
	*L = sm_alloc();
	*R = sm_alloc();
	for(prow = A->first_row; prow != 0; prow = prow->next_row) {
	    if (prow->flag) {
		copy_row(*L, prow);
	    } else {
		copy_row(*R, prow);
	    }
	}
	return 1;
    }
}
