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/**************************************************************************
* *
* Regina - A Normal Surface Theory Calculator *
* Computational Engine *
* *
* Copyright (c) 1999-2025, Ben Burton *
* For further details contact Ben Burton (bab@debian.org). *
* *
* This program is free software; you can redistribute it and/or *
* modify it under the terms of the GNU General Public License as *
* published by the Free Software Foundation; either version 2 of the *
* License, or (at your option) any later version. *
* *
* As an exception, when this program is distributed through (i) the *
* App Store by Apple Inc.; (ii) the Mac App Store by Apple Inc.; or *
* (iii) Google Play by Google Inc., then that store may impose any *
* digital rights management, device limits and/or redistribution *
* restrictions that are required by its terms of service. *
* *
* This program is distributed in the hope that it will be useful, but *
* WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU *
* General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with this program. If not, see <https://www.gnu.org/licenses/>. *
* *
**************************************************************************/
#include <queue>
#include "surface/disc.h"
#include "surface/normalsurface.h"
namespace regina {
std::vector<NormalSurface> NormalSurface::components() const {
if (connected_.has_value() && *connected_) {
// We already know that either the surface is empty or it is a
// single connected component.
if (isEmpty())
return {};
else
return { *this };
}
// Shamelessly copied from my orientation/two-sidedness code from
// years earlier. Some day I will need to make a generic structure
// for a depth-first search over normal discs. Not today.
// If the precondition (compactness) does not hold, things will get
// nasty (read: infinite).
if (! isCompact())
return {};
// TODO: First check that there aren't too many discs!
// The components structure stores an integer alongside each disc;
// that integer will be the ID of its connected component, or -1 if
// this is unknown. Components are numbered from 0 upwards.
DiscSetSurfaceData<long> components(*this, -1);
// Stores the component ID for each disc.
std::queue<DiscSpec> discQueue;
// A queue of discs whose component IDs must be propagated.
DiscSpecIterator it(components);
// Runs through the discs whose component IDs might not have yet
// been determined.
DiscSpec use;
// The disc that currently holds our interest.
int nGluingArcs; // The number of arcs on the current disc to
// which an adjacent disc might may be glued.
Perm<4> arc[8]; // Holds each gluing arc for the current disc.
long compID = 0; // The current working component ID.
long i;
while (true) {
// If there's no discs to propagate from, choose the next
// one without a component label.
while (discQueue.empty() && (! it.done())) {
if (components.data(*it) == -1) {
components.data(*it) = compID++;
discQueue.push(*it);
}
++it;
}
if (discQueue.empty())
break;
// At the head of the queue is the next already-labelled disc
// whose component ID must be propagated.
use = discQueue.front();
discQueue.pop();
// Determine along which arcs we may glue other discs.
if (use.type < 4) {
// Current disc is a triangle.
nGluingArcs = 3;
for (i = 0; i < 3; i++)
arc[i] = regina::triDiscArcs[use.type][i];
} else if (use.type < 7) {
// Current disc is a quad.
nGluingArcs = 4;
for (i = 0; i < 4; i++)
arc[i] = regina::quadDiscArcs[use.type - 4][i];
} else {
// Current disc is an octagon.
nGluingArcs = 8;
for (i = 0; i < 8; i++)
arc[i] = regina::octDiscArcs[use.type - 7][i];
}
// Process any discs that might be adjacent to each of these
// gluing arcs.
for (i = 0; i < nGluingArcs; ++i) {
// Establish which is the adjacent disc.
auto adjDisc = components.adjacentDisc(use, arc[i]);
if (! adjDisc)
continue;
// There is actually a disc glued along this arc.
// Propagate the component ID.
if (components.data(adjDisc->first) == -1) {
components.data(adjDisc->first) = components.data(use);
discQueue.push(adjDisc->first);
}
}
}
// Were there any discs at all?
if (compID == 0) {
connected_ = true;
return {};
}
// Create the set of normal surfaces!
// Note that all vectors are automagically initialised to zero.
std::vector<NormalSurface> dest;
std::vector<Vector<LargeInteger>> ans;
ans.reserve(compID);
if (couldBeAlmostNormal()) {
size_t size = 10 * triangulation_->size();
for (i = 0; i < compID; ++i)
ans.emplace_back(size);
for (const auto& disc : components)
++ans[components.data(disc)][10 * disc.tetIndex + disc.type];
for (i = 0; i < compID; ++i)
dest.emplace_back(triangulation_, NormalCoords::AlmostNormal,
ans[i]);
} else {
size_t size = 7 * triangulation_->size();
for (i = 0; i < compID; ++i)
ans.emplace_back(size);
for (const auto& disc : components)
++ans[components.data(disc)][7 * disc.tetIndex + disc.type];
for (i = 0; i < compID; ++i)
dest.emplace_back(triangulation_, NormalCoords::Standard, ans[i]);
}
connected_ = (compID == 1);
return dest;
}
bool NormalSurface::disjoint(const NormalSurface& other) const {
// Some sanity tests before we begin.
// These should all pass if the user has adhered to the preconditions.
if (! (isCompact() && other.isCompact()))
return false;
if (! (isConnected() && other.isConnected()))
return false;
// Begin with a local compatibility test.
if (! locallyCompatible(other))
return false;
// Now we know that the sum of both surfaces is an embedded surface.
// Form the sum, pull it apart into connected components, and see
// whether we get our original two surfaces back.
//
// Note: components() may return surfaces that use
// different vector encodings, but equality testing can handle this.
std::vector<NormalSurface> bits = ((*this) + other).components();
return (bits.size() == 2 && ((*this) == bits[0] || (*this) == bits[1]));
}
} // namespace regina
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