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101 lines
3.2 KiB
C++
101 lines
3.2 KiB
C++
#ifndef XRPL_ALGORITHM_H_INCLUDED
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#define XRPL_ALGORITHM_H_INCLUDED
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#include <utility>
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namespace xrpl {
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// Requires: [first1, last1) and [first2, last2) are ordered ranges according to
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// comp.
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// Effects: For each pair of elements {i, j} in the intersection of the sorted
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// sequences [first1, last1) and [first2, last2), perform action(i, j).
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// Note: This algorithm is evolved from std::set_intersection.
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template <class InputIter1, class InputIter2, class Action, class Comp>
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void
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generalized_set_intersection(
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InputIter1 first1,
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InputIter1 last1,
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InputIter2 first2,
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InputIter2 last2,
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Action action,
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Comp comp)
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{
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while (first1 != last1 && first2 != last2)
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{
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if (comp(*first1, *first2)) // if *first1 < *first2
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++first1; // then reduce first range
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else
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{
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if (!comp(*first2, *first1)) // if *first1 == *first2
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{ // then this is an intersection
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action(*first1, *first2); // do the action
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++first1; // reduce first range
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}
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++first2; // Reduce second range because *first2 <= *first1
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}
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}
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}
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// Requires: [first1, last1) and [first2, last2) are ordered ranges according to
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// comp.
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// Effects: Eliminates all the elements i in the range [first1, last1) which are
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// equivalent to some value in [first2, last2) or for which pred(i) returns
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// true.
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// Returns: A FwdIter1 E such that [first1, E) is the range of elements not
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// removed by this algorithm.
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// Note: This algorithm is evolved from std::remove_if and
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// std::set_intersection.
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template <class FwdIter1, class InputIter2, class Pred, class Comp>
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FwdIter1
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remove_if_intersect_or_match(
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FwdIter1 first1,
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FwdIter1 last1,
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InputIter2 first2,
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InputIter2 last2,
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Pred pred,
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Comp comp)
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{
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// [original-first1, current-first1) is the set of elements to be preserved.
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// [current-first1, i) is the set of elements that have been removed.
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// [i, last1) is the set of elements not tested yet.
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// Test each *i in [first1, last1) against [first2, last2) and pred
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for (auto i = first1; i != last1;)
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{
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// if (*i is not in [first2, last2)
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if (first2 == last2 || comp(*i, *first2))
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{
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if (!pred(*i))
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{
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// *i should not be removed, so append it to the preserved set
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if (i != first1)
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*first1 = std::move(*i);
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++first1;
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}
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// *i has been fully tested, prepare for next i by
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// appending i to the removed set, whether or not
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// it has been moved from above.
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++i;
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}
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else // *i might be in [first2, last2) because *i >= *first2
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{
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if (!comp(*first2, *i)) // if *i == *first2
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++i; // then append *i to the removed set
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// All elements in [i, last1) are known to be greater than *first2,
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// so reduce the second range.
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++first2;
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}
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// Continue to test *i against [first2, last2) and pred
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}
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return first1;
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}
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} // namespace xrpl
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#endif
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