struct answer solve(int t, int k)
{
if (t < 0) {
/* twig */
int ball = (t == -2);
switch (k) {
case 0: return (struct answer) { 0, (ball ? 0 : 1) };
case 1: return (struct answer) { (ball ? 0 : 1), -1 };
default: return (struct answer) { -1, -1 };
}
} else {
/* internal node */
struct answer a0 = solve(tree[t][0], k / 2);
struct answer a1 = solve(tree[t][1], k / 2);
if (k % 2 == 0) {
return (struct answer) {
aplus(a0.a, a1.a),
amin(aplus(a0.a, a1.b), aplus(a0.b, a1.a)) };
} else {
return (struct answer) {
amin(aplus(a0.a, a1.b), aplus(a0.b, a1.a)),
aplus(a0.b, a1.b) };
}
}
}
int main(void)
{
while (fgets(buf, sizeof(buf), stdin) != NULL) {
bufp = 0;
nnode = 0;
ntwig = 0;
nball = 0;
int root = parse();
assert(root == 0);
assert(buf[bufp] == '\n' && buf[bufp+1] == '\0');
assert(ntwig >= MINTWIGS && ntwig <= MAXTWIGS);
struct answer answer = solve(root, nball);
if (answer.a >= 0)
printf("%d\n", answer.a);
else
printf("impossible\n");
}
return 0;
}
double SBVAR::LogLikelihood(void)
{
double log_likelihood=log_likelihood_constant + lambda_T*LogAbsDeterminant(A0);
TDenseVector a0(n_vars), aplus(n_predetermined);
for (int i=n_vars-1; i >= 0; i--)
{
a0.RowVector(A0,i);
aplus.RowVector(Aplus,i);
log_likelihood+=-0.5*(InnerProduct(a0,a0,YY) - 2.0*InnerProduct(aplus,a0,XY) + InnerProduct(aplus,aplus,XX));
}
return log_likelihood;
}
double SBVAR_symmetric::LogPrior(void)
{
if (flat_prior) return 0.0;
double log_prior=log_prior_constant;
TDenseVector a0(n_vars), aplus(n_predetermined);
for (int i=n_vars-1; i >= 0; i--)
{
a0.RowVector(A0,i);
aplus.RowVector(Aplus,i);
log_prior+=-0.5*(InnerProduct(a0,a0,prior_YY) - 2.0*InnerProduct(aplus,a0,prior_XY) + InnerProduct(aplus,aplus,prior_XX));
}
return log_prior;
}
