knapsack.c
3.17 KB
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/* knapsack */
/* knapsack(X, Y) == min(Y) <= sum(X) <= max(Y) */
// XXX: assumes all values are non-negative
static int fd_knapsack_propagate2(fd_constraint this, fd_int culprit)
{
int ub, lb;
int min, max;
int terms = this->nvariables - 1;
int i;
// XXX: ignoring culprit
lb = _fd_var_min(VAR(this, this->nvariables - 1)); // lower bound
ub = _fd_var_max(VAR(this, this->nvariables - 1)); // upper bound
// sum the minima of the variables' domains
min = 0;
for (i = 0; i < terms; ++i)
{
min += _fd_var_min(VAR(this, i));
if (min > ub)
return FD_NOSOLUTION;
}
// sum the maxima of the variables' domains
max = 0;
for (i = 0; i < terms; ++i)
max += _fd_var_max(VAR(this, i));
if (max < lb)
return FD_NOSOLUTION;
// XXX: poor man's propagation
if (min == ub)
for (i = 0; i < terms; ++i)
{
int min_x = _fd_var_min(VAR(this, i));
int min_y = _fd_var_min(VAR(this, terms + i));
int changed_x = 0, changed_y = 0;
if (min_x != 0 || min_y != 0)
if (min_x == 0)
{
if (_fd_var_del_gt(0, VAR(this, i)))
_fd_revise_connected(this, VAR(this, i));
}
else if (min_y == 0)
{
if (_fd_var_del_gt(0, VAR(this, terms + i)))
_fd_revise_connected(this, VAR(this, terms + i));
}
else // min_x != 0 && min_y != 0
{
if (_fd_var_del_gt(min_x, VAR(this, i)))
_fd_revise_connected(this, VAR(this, i));
if (_fd_var_del_gt(min_y, VAR(this, terms + i)))
_fd_revise_connected(this, VAR(this, terms + i));
}
}
else if (max == lb)
for (i = 0; i < terms; ++i)
{
int max_x = _fd_var_max(VAR(this, i));
int max_y = _fd_var_max(VAR(this, terms + i));
int changed_x = 0, changed_y = 0;
if (max_x != 0 || max_y != 0)
if (max_x == 0)
{
if (_fd_var_del_lt(0, VAR(this, i))) // XXX: delete < 0???
_fd_revise_connected(this, VAR(this, i));
}
else if (max_y == 0)
{
if (_fd_var_del_lt(0, VAR(this, terms + i))) // XXX: delete < 0???
_fd_revise_connected(this, VAR(this, terms + i));
}
else // max_x != 0 && max_y != 0
{
if (_fd_var_del_lt(max_x, VAR(this, i)))
_fd_revise_connected(this, VAR(this, i));
if (_fd_var_del_lt(max_y, VAR(this, terms + i)))
_fd_revise_connected(this, VAR(this, terms + i));
}
}
if (_fd_var_del_lt(min, VAR(this, this->nvariables - 1)) |
_fd_var_del_gt(max, VAR(this, this->nvariables - 1)))
{
if (fd_domain_empty(VAR(this, this->nvariables - 1)))
return FD_NOSOLUTION;
_fd_revise_connected(this, VAR(this, this->nvariables - 1));
}
return FD_OK;
}
fd_constraint fd_knapsack(fd_int variables[], int nvariables, fd_int limits)
{
fd_constraint c = _fd_constraint_new(nvariables + 1, 0);
int i;
if (c)
{
for (i = 0; i < nvariables; ++i)
c->variables[i] = FD_INT2C_VAR(variables[i]);
c->variables[nvariables] = FD_INT2C_VAR(limits);
#ifdef CONSTRAINT_CLASS
c->kind = FD_CONSTR_KNAPSACK;
#else /* CONSTRAINT_CLASS */
c->propagator2 = fd_knapsack_propagate2;
#endif /* CONSTRAINT_CLASS */
for (i = 0; i < c->nvariables; ++i)
_fd_var_add_constraint(VAR(c, i), c);
_fd_add_constraint(c);
}
return c;
}