71 lines
2.2 KiB
C++
71 lines
2.2 KiB
C++
#pragma once
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#include <vector>
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#include <algorithm>
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namespace algo {
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template<typename Iterator, typename Comparator>
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void merge(Iterator start, Iterator middle, Iterator end, Comparator cmp, Iterator output_start) {
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Iterator start_m = start;
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Iterator start2 = middle + 1;
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//merge from input until one half completes
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while (start <= middle && start2 <= end) {
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if (cmp(*start, *start2)) {
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*output_start = *start;
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start++;
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} else {
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*output_start = *start2;
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start2++;
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}
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output_start++;
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}
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//try to finish first half
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while (start <= middle) {
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*output_start = *start;
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start++;
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output_start++;
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}
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while (start2 <= end) {
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*output_start = *start2;
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start2++;
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output_start++;
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}
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const auto nit = std::distance(start_m, end);
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for (auto i = 0; i <= nit; i++, start_m++, output_start++) {
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*start_m = *output_start;
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}
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}
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template<typename Container, typename Iterator, typename Comparator>
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void mergesort_splitup(Container &output_vec, Iterator start, Iterator end, Comparator cmp, Iterator output_start) {
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Iterator middle = start;
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Iterator output_started_from = output_start;
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//move middle iterator litterally to the middle
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std::advance(middle, std::distance(start, end) / 2);
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//sort the first half within an recursion
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mergesort_splitup(output_vec, start, middle, cmp, output_start);
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//move output iterator
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std::advance(output_start, std::distance(start, middle + 1));
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//sort the second half within a recursion
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mergesort_splitup(output_vec, middle + 1, end, cmp, output_start);
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//merge everything together starting from the complete beginning
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merge(start, middle, end, cmp, output_started_from);
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}
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template<typename Iterator, typename Comparator>
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void mergesort(Iterator start, Iterator end, Comparator cmp) {
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using valtype = typename std::iterator_traits<Iterator>::value_type;
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std::vector<valtype> output_vec(std::distance(start, end));
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}
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} |