// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// File: algorithm.h
// -----------------------------------------------------------------------------
//
// This header file contains Google extensions to the standard <algorithm> C++
// header.
#ifndef ABSL_ALGORITHM_ALGORITHM_H_
#define ABSL_ALGORITHM_ALGORITHM_H_
#include <algorithm>
#include <iterator>
#include <type_traits>
namespace absl {
namespace algorithm_internal {
// Performs comparisons with operator==, similar to C++14's `std::equal_to<>`.
struct EqualTo {
template <typename T, typename U>
bool operator()(const T& a, const U& b) const {
return a == b;
}
};
template <typename InputIter1, typename InputIter2, typename Pred>
bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2, Pred pred, std::input_iterator_tag,
std::input_iterator_tag) {
while (true) {
if (first1 == last1) return first2 == last2;
if (first2 == last2) return false;
if (!pred(*first1, *first2)) return false;
++first1;
++first2;
}
}
template <typename InputIter1, typename InputIter2, typename Pred>
bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2, Pred&& pred, std::random_access_iterator_tag,
std::random_access_iterator_tag) {
return (last1 - first1 == last2 - first2) &&
std::equal(first1, last1, first2, std::forward<Pred>(pred));
}
// When we are using our own internal predicate that just applies operator==, we
// forward to the non-predicate form of std::equal. This enables an optimization
// in libstdc++ that can result in std::memcmp being used for integer types.
template <typename InputIter1, typename InputIter2>
bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2, algorithm_internal::EqualTo /* unused */,
std::random_access_iterator_tag,
std::random_access_iterator_tag) {
return (last1 - first1 == last2 - first2) &&
std::equal(first1, last1, first2);
}
template <typename It>
It RotateImpl(It first, It middle, It last, std::true_type) {
return std::rotate(first, middle, last);
}
template <typename It>
It RotateImpl(It first, It middle, It last, std::false_type) {
std::rotate(first, middle, last);
return std::next(first, std::distance(middle, last));
}
} // namespace algorithm_internal
// Compares the equality of two ranges specified by pairs of iterators, using
// the given predicate, returning true iff for each corresponding iterator i1
// and i2 in the first and second range respectively, pred(*i1, *i2) == true
//
// This comparison takes at most min(`last1` - `first1`, `last2` - `first2`)
// invocations of the predicate. Additionally, if InputIter1 and InputIter2 are
// both random-access iterators, and `last1` - `first1` != `last2` - `first2`,
// then the predicate is never invoked and the function returns false.
//
// This is a C++11-compatible implementation of C++14 `std::equal`. See
// https://en.cppreference.com/w/cpp/algorithm/equal for more information.
template <typename InputIter1, typename InputIter2, typename Pred>
bool equal(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2, Pred&& pred) {
return algorithm_internal::EqualImpl(
first1, last1, first2, last2, std::forward<Pred>(pred),
typename std::iterator_traits<InputIter1>::iterator_category{},
typename std::iterator_traits<InputIter2>::iterator_category{});
}
// Performs comparison of two ranges specified by pairs of iterators using
// operator==.
template <typename InputIter1, typename InputIter2>
bool equal(InputIter1 first1, InputIter1 last1, InputIter2 first2,
InputIter2 last2) {
return absl::equal(first1, last1, first2, last2,
algorithm_internal::EqualTo{});
}
// Performs a linear search for `value` using the iterator `first` up to
// but not including `last`, returning true if [`first`, `last`) contains an
// element equal to `value`.
//
// A linear search is of O(n) complexity which is guaranteed to make at most
// n = (`last` - `first`) comparisons. A linear search over short containers
// may be faster than a binary search, even when the container is sorted.
template <typename InputIterator, typename EqualityComparable>
bool linear_search(InputIterator first, InputIterator last,
const EqualityComparable& value) {
return std::find(first, last, value) != last;
}
// Performs a left rotation on a range of elements (`first`, `last`) such that
// `middle` is now the first element. `rotate()` returns an iterator pointing to
// the first element before rotation. This function is exactly the same as
// `std::rotate`, but fixes a bug in gcc
// <= 4.9 where `std::rotate` returns `void` instead of an iterator.
//
// The complexity of this algorithm is the same as that of `std::rotate`, but if
// `ForwardIterator` is not a random-access iterator, then `absl::rotate`
// performs an additional pass over the range to construct the return value.
template <typename ForwardIterator>
ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
ForwardIterator last) {
return algorithm_internal::RotateImpl(
first, middle, last,
std::is_same<decltype(std::rotate(first, middle, last)),
ForwardIterator>());
}
} // namespace absl
#endif // ABSL_ALGORITHM_ALGORITHM_H_
