63 lines
1.6 KiB
C++
63 lines
1.6 KiB
C++
#ifndef OSRM_UTIL_PERMUTATION_HPP
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#define OSRM_UTIL_PERMUTATION_HPP
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#include "util/integer_range.hpp"
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#include <vector>
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namespace osrm
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{
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namespace util
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{
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template <typename RandomAccesIterator, typename IndexT>
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void inplacePermutation(RandomAccesIterator begin,
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RandomAccesIterator end,
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const std::vector<IndexT> &old_to_new)
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{
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std::size_t size = std::distance(begin, end);
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BOOST_ASSERT(old_to_new.size() == size);
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// we need a little bit auxililary space since we need to mark
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// replaced elements in a non-destructive way
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std::vector<bool> was_replaced(size, false);
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for (auto index : util::irange<IndexT>(0, size))
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{
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if (was_replaced[index])
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{
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continue;
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}
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if (old_to_new[index] == index)
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{
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was_replaced[index] = true;
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continue;
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}
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// iterate over a cycle in the permutation
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auto buffer = begin[index];
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auto old_index = index;
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auto new_index = old_to_new[old_index];
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for (; new_index != index; old_index = new_index, new_index = old_to_new[new_index])
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{
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was_replaced[old_index] = true;
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std::swap(buffer, begin[new_index]);
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}
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was_replaced[old_index] = true;
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std::swap(buffer, begin[index]);
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}
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}
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template <typename IndexT>
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std::vector<IndexT> orderingToPermutation(const std::vector<IndexT> &ordering)
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{
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std::vector<std::uint32_t> permutation(ordering.size());
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for (auto index : util::irange<std::uint32_t>(0, ordering.size()))
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permutation[ordering[index]] = index;
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return permutation;
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}
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}
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}
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#endif
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