forked from boostorg/algorithm
100 lines
3.6 KiB
Plaintext
100 lines
3.6 KiB
Plaintext
[/ File find_backward.qbk]
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[section:find_backward find_backward ]
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[/license
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Copyright (c) 2018 T. Zachary Laine
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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]
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The header file 'find_backward.hpp' contains variants of the stl algorithm
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`find`. These variants are like `find`, except that the evaluate the elements
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of the given sequence if reverse order.
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Consider how finding the last element that is equal to `x` in a range is
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typically done:
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// Assume a valid range if elements delimited by [first, last).
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while (last-- != first) {
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if (*last == x) {
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// Use last here...
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}
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}
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Raw loops are icky though. PErhaps we should do a bit of extra work to allow
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the use of `std::find()`:
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auto rfirst = std::make_reverse_iterator(last);
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auto rlast = std::make_reverse_iterator(first);
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auto it = std::find(rfirst, rlast);
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// Use it here...
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That seems nicer, but it has two major drawbacks. First, it requires an
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unpleasant amount of typing. Second, it is considerably less efficient than
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forward-iterator `find` , since `std::reverse_iterator` calls its
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base-iterator's `operator--()` in most of its members before doing the work
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that the member requires.
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[heading interface]
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template<typename BidiIter, typename T>
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BidiIter find_backward(BidiIter first, BidiIter last, T const & x);
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The function `find_backward` returns an iterator to the last element of
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`[first, last)` that is equal to `x`.
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template<typename BidiIter, typename T>
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BidiIter find_not_backward(BidiIter first, BidiIter last, T const & x);
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The function `find_not_backward` returns an iterator to the last element of
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`[first, last)` that is not equal to `x`.
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template<typename BidiIter, typename Pred>
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BidiIter find_if_backward(BidiIter first, BidiIter last, Pred p);
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The function `find_if_backward` returns an iterator to the last element of
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`[first, last)` for which `pred` returns `true`.
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template<typename BidiIter, typename Pred>
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BidiIter find_if_not_backward(BidiIter first, BidiIter last, Pred p);
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The function `find_if_not_backward` returns an iterator to the last element of
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`[first, last)` for which `pred` returns `false`.
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[heading Examples]
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Given the container `c1` containing `{ 2, 1, 2 }`, then
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find_backward ( c1.begin(), c1.end(), 2 ) --> --c1.end()
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find_backward ( c1.begin(), c1.end(), 3 ) --> c1.end()
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find_if_backward ( c1.begin(), c1.end(), [](int i) {return i == 2;} ) --> --c1.end()
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find_if_backward ( c1.begin(), c1.end(), [](int i) {return i == 3;} ) --> c1.end()
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find_not_backward ( c1.begin(), c1.end(), 2 ) --> std::prev(c1.end(), 2)
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find_not_backward ( c1.begin(), c1.end(), 1 ) --> c1.end()
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find_if_not_backward ( c1.begin(), c1.end(), [](int i) {return i == 2;} ) --> std::prev(c1.end(), 2)
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find_if_not_backward ( c1.begin(), c1.end(), [](int i) {return i == 1;} ) --> c1.end()
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[heading Iterator Requirements]
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All variants work on bidirectional iterators.
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[heading Complexity]
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Linear.
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[heading Exception Safety]
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All of the variants take their parameters by value and do not depend upon any
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global state. Therefore, all the routines in this file provide the strong
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exception guarantee.
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[endsect]
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[/ File equal.qbk
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Copyright 2018 T. Zachary Laine
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt).
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]
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