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#include "rst.h"
using namespace std;
// David B. Wilson. Generating Random Spanning Trees More Quickly than the Cover Time.
TreeSampler::TreeSampler(const ArcFactoredForest& af) : forest(af), usucc(af.size() + 1) {
// edges are directed from modifiers to heads, to the root
for (int m = 1; m <= forest.size(); ++m) {
SampleSet<double>& ss = usucc[m];
for (int h = 0; h <= forest.size(); ++h)
ss.add(forest(h-1,m-1).edge_prob.as_float());
}
}
void TreeSampler::SampleRandomSpanningTree(EdgeSubset* tree) {
MT19937 rng;
const int r = 0;
bool success = false;
while (!success) {
int roots = 0;
vector<int> next(forest.size() + 1, -1);
vector<char> in_tree(forest.size() + 1, 0);
in_tree[r] = 1;
for (int i = 0; i < forest.size(); ++i) {
int u = i;
if (in_tree[u]) continue;
while(!in_tree[u]) {
next[u] = rng.SelectSample(usucc[u]);
u = next[u];
}
u = i;
cerr << (u-1);
while(!in_tree[u]) {
in_tree[u] = true;
u = next[u];
cerr << " > " << (u-1);
if (u == r) { ++roots; }
}
cerr << endl;
}
assert(roots > 0);
if (roots > 1) {
cerr << "FAILURE\n";
} else {
success = true;
}
}
};
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