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AK: Make single pivot quick_sort guarantee a max stack depth of log(n)
- The change to quick_sort requires SimpleIterator to support assignment. - Rename quick_sort to single_pivot_quick_sort to make it easier to choose a specific implementation (not based on signature). - Ensure single_pivot_quick_sort does not copy the pivots - Expand sorts_without_copy test case to cover both single and dual pivot implementations.
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3 changed files with 105 additions and 19 deletions
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@ -86,35 +86,50 @@ void dual_pivot_quick_sort(Collection& col, int start, int end, LessThan less_th
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}
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template<typename Iterator, typename LessThan>
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void quick_sort(Iterator start, Iterator end, LessThan less_than)
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void single_pivot_quick_sort(Iterator start, Iterator end, LessThan less_than)
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{
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int size = end - start;
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if (size <= 1)
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return;
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for (;;) {
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int size = end - start;
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if (size <= 1)
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return;
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int pivot_point = size / 2;
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auto pivot = *(start + pivot_point);
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int pivot_point = size / 2;
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if (pivot_point)
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swap(*(start + pivot_point), *start);
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if (pivot_point)
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swap(*(start + pivot_point), *start);
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auto&& pivot = *start;
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int i = 1;
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for (int j = 1; j < size; ++j) {
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if (less_than(*(start + j), pivot)) {
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swap(*(start + j), *(start + i));
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++i;
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int i = 1;
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for (int j = 1; j < size; ++j) {
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if (less_than(*(start + j), pivot)) {
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swap(*(start + j), *(start + i));
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++i;
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}
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}
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swap(*start, *(start + i - 1));
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// Recur into the shorter part of the remaining data
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// to ensure a stack depth of at most log(n).
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if (i > size / 2) {
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single_pivot_quick_sort(start + i, end, less_than);
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end = start + i - 1;
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} else {
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single_pivot_quick_sort(start, start + i - 1, less_than);
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start = start + i;
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}
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}
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swap(*start, *(start + i - 1));
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quick_sort(start, start + i - 1, less_than);
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quick_sort(start + i, end, less_than);
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}
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template<typename Iterator>
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void quick_sort(Iterator start, Iterator end)
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{
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quick_sort(start, end, [](auto& a, auto& b) { return a < b; });
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single_pivot_quick_sort(start, end, [](auto& a, auto& b) { return a < b; });
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}
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template<typename Iterator, typename LessThan>
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void quick_sort(Iterator start, Iterator end, LessThan less_than)
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{
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single_pivot_quick_sort(start, end, move(less_than));
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}
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template<typename Collection, typename LessThan>
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