static void backtrack(int *out, int *rowsum, int *colsum, int fill,
int nr, int nc, int *rfill, int *cfill, int *ind)
{
int tmp, i, j, k, ir, ic;
int izero = nr * nc - 1, ielig = nr * nc - 1, npick = 0, oldpick = 0,
ndrop = 1, dropouts[BACKSTEP], idrop = 0, lastpick = 0;
/* initialize */
for(i = 0; i < nr * nc; i++)
ind[i] = i;
memset(rfill, 0, nr * sizeof(int));
memset(cfill, 0, nc * sizeof(int));
/* check for empty rows/columns and move their indices from eligible */
for (ir=0; ir < nr; ir++)
if (rowsum[ir] <= 0)
for (i = ielig; i > EMPTY; i--)
if (ind[i] % nr == ir) {
SWAP(ind[i], ind[ielig]);
ielig--;
}
for (ic=0; ic < nc; ic++)
if (colsum[ic] <= 0)
for (i = ielig; i > EMPTY; i--)
if (ind[i] / nr == ic) {
SWAP(ind[i], ind[ielig]);
ielig--;
}
/* Start working */
while(npick < fill) { /* outermost loop (placeholder) */
/* fill */
#if LOUD
Rprintf("\nFILL ");
#endif
while(ielig > EMPTY) {
i = IRAND(ielig); /* eligible: always succeed */
#if LOUD
Rprintf("pick %d ", i);
#endif
ir = ind[i] % nr; /* row */
ic = ind[i] / nr; /* column */
npick++;
SWAP(ind[i], ind[ielig]); /* move after izero */
if (ielig < izero) {
SWAP(ind[ielig], ind[izero]);
}
ielig--;
izero--;
/* update fills and move from eligible if marginal sum reached */
if (++rfill[ir] == rowsum[ir])
for(i = ielig; i > EMPTY; i--)
if (ind[i] % nr == ir) {
#if LOUD
Rprintf("ban %d ", i);
#endif
SWAP(ind[i], ind[ielig]);
ielig--;
}
if (++cfill[ic] == colsum[ic])
for (i = ielig; i > EMPTY; i--)
if (ind[i] / nr == ic) {
#if LOUD
Rprintf("ban %d ", i);
#endif
SWAP(ind[i], ind[ielig]);
ielig--;
}
}
/* get out */
#if LOUD
if (npick != oldpick) Rprintf("\n*** PICKED %d ", npick);
#endif
R_CheckUserInterrupt();
if (npick == fill)
break;
#if RESET
/* if we did worse than previously, undo: remove picked items
* and put back the ones removed as dropouts */
if (npick < oldpick) {
#if LOUD
Rprintf("\nRESET ");
#endif
/* first items after izero were added in the last cycle --
* these should be removed except for the originally
* dropped items (dropouts) that should be kept */
lastpick = izero + ndrop - oldpick + npick;
for (i = izero+1; i <= lastpick; i++) {
k = imatch(ind[i], dropouts, idrop+1);
if (k == EMPTY) { /* remove pick: not a dropout */
#if LOUD
Rprintf("drop %d ", i);
#endif
rfill[ind[i] % nr]--;
cfill[ind[i] / nr]--;
npick--;
izero++;
if (izero < i) {
SWAP(ind[i], ind[izero]);
}
} else { /* remove from dropouts */
#if LOUD
Rprintf("keep %d ", i);
#endif
dropouts[k] = dropouts[idrop--];
}
}
/* The dropouts are among first items of ind: search these and
* add back to picked. */
i = EMPTY;
while(idrop > EMPTY) {
k = imatch(ind[++i], dropouts, idrop+1);
if (k != EMPTY) { /* pick back this item */
#if LOUD
Rprintf("pick %d ", i);
#endif
rfill[ind[i] % nr]++;
cfill[ind[i] / nr]++;
SWAP(ind[i], ind[izero]);
izero--;
npick++;
dropouts[k] = dropouts[idrop--];
}
}
}
#endif /* RESET */
/* backtrack: remove picked items and update marginal totals
* and see if any items become eligible. If 'npick' did not
* improve from the best 'oldpick', increase 'ndrop' up to
* BACKSTEP, and reset 'ndrop' to 1 if 'npick' improved. */
if (oldpick < npick) {
ndrop = 1;
oldpick = npick;
} else if (ndrop < BACKSTEP && ndrop < npick) {
ndrop++;
}
#if LOUD
Rprintf("\nBACKTRACK %d: ", ndrop);
#endif
for (j = 0, idrop = EMPTY; j < ndrop; j++) {
i = IRAND(npick-1) + izero + 1;
#if LOUD
Rprintf("%d ", i);
#endif
dropouts[++idrop] = ind[i]; /* save removed */
rfill[ind[i] % nr]--;
cfill[ind[i] / nr]--;
npick--;
ielig++;
izero++;
SWAP(ind[i], ind[izero]);
SWAP(ind[izero], ind[ielig]); /* if elig is EMPTY: move to ind[0] */
}
/* see what can be moved to eligible */
for (i = izero; i > ielig; i--) {
ir = ind[i] % nr;
ic = ind[i] / nr;
if (rfill[ir] < rowsum[ir] && cfill[ic] < colsum[ic]) {
#if LOUD
Rprintf("free %d ", i);
#endif
ielig++;
SWAP(ind[i], ind[ielig]);
}
}
}
/* output */
memset(out, 0, nr * nc * sizeof(int));
/* put 1's in their places */
for (i = izero+1; i < nr*nc; i++)
out[ind[i]] = 1;
}
inline static dt::boolean call(const dt::istring &pattern, const dt::istring &haystack) {
return imatch(pattern, haystack);
}
