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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Inkscape::Algorithms::nearest_common_ancestor
*
* Authors:
* MenTaLguY <mental@rydia.net>
*
* Copyright (C) 2004 MenTaLguY
*
* Released under GNU GPL v2+, read the file 'COPYING' for more information.
*/
#ifndef SEEN_INKSCAPE_ALGORITHMS_NEAREST_COMMON_ANCESTOR_H
#define SEEN_INKSCAPE_ALGORITHMS_NEAREST_COMMON_ANCESTOR_H
#include <iterator>
#include <functional>
namespace Inkscape {
namespace Algorithms {
/**
* Time costs:
*
* The case of sharing a common successor is handled in O(1) time.
*
* If \a a is the nearest common ancestor, then runs in O(len(rest of b)) time.
*
* Otherwise, runs in O(len(a) + len(b)) time.
*/
template <typename ForwardIterator>
ForwardIterator nearest_common_ancestor(ForwardIterator a, ForwardIterator b, ForwardIterator end)
{
if ( a == end || b == end ) {
return end;
}
/* Handle in O(1) time the common cases of identical lists or tails. */
{
/* identical lists? */
if ( a == b ) {
return a;
}
/* identical tails? */
ForwardIterator tail_a(a);
ForwardIterator tail_b(b);
if ( ++tail_a == ++tail_b ) {
return tail_a;
}
}
/* Build parallel lists of suffixes, ordered by increasing length. */
ForwardIterator lists[2] = { a, b };
std::vector<ForwardIterator> suffixes[2];
for ( int i=0 ; i < 2 ; i++ ) {
for ( ForwardIterator iter(lists[i]) ; iter != end ; ++iter ) {
if ( iter == lists[1-i] ) {
// the other list is a suffix of this one
return lists[1-i];
}
suffixes[i].push_back(iter);
}
}
/* Iterate in parallel through the lists of suffix lists from shortest to
* longest, stopping before the first pair of suffixes that differs
*/
ForwardIterator longest_common(end);
while ( !suffixes[0].empty() && !suffixes[1].empty() &&
suffixes[0].back() == suffixes[1].back() )
{
longest_common = suffixes[0].back();
suffixes[0].pop_back();
suffixes[1].pop_back();
}
return longest_common;
}
}
}
#endif /* !SEEN_INKSCAPE_ALGORITHMS_NEAREST_COMMON_ANCESTOR_H */
/*
Local Variables:
mode:c++
c-file-style:"stroustrup"
c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
indent-tabs-mode:nil
fill-column:99
End:
*/
// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4 :
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