std::is_partitioned

C++ Reference
Language Concepts Utilities library Strings library Containers library Algorithms library Iterators library Numerics library Input/output library Localizations library Regular expressions library (C++11) Atomic operations library (C++11) Thread support library (C++11)
Algorithm library
Functions Non-modifying sequence operations all_of any_of none_of (C++11) (C++11) (C++11) for_each count count_if mismatch equal find find_if find_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations copy copy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n remove remove_if remove_copy remove_copy_if replace replace_if replace_copy replace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffle shuffle   (C++11) unique unique_copy Partitioning operations is_partitioned (C++11) partition partition_copy (C++11) stable_partition partition_point (C++11) Sorting operations (on sorted ranges) is_sorted (C++11) is_sorted_until (C++11) sort partial_sort partial_sort_copy stable_sort nth_element Binary search operations (on sorted ranges) lower_bound upper_bound binary_search equal_range Set operations (on sorted ranges) merge inplace_merge includes set_difference set_intersection set_symmetric_difference set_union Heap operations is_heap is_heap_until (C++11) make_heap push_heap pop_heap sort_heap Minimum/maximum operations max max_element min min_element minmax (C++11) minmax_element (C++11) lexicographical_compare is_permutation (C++11) next_permutation prev_permutation Numeric operations iota (C++11) accumulate inner_product adjacent_difference partial_sum C library qsort bsearch

Defined in header <algorithm>
template< class InputIterator, class UnaryPredicate > bool is_partitioned( InputIterator first, InputIterator last, UnaryPredicate p );		(since C++11)

Returns true if all elements in the range [first, last) that satisfy the predicate p appear before all elements that don't. Also returns true if [first, last) is empty.

Parameters

first, last	-	the range of elements to check
p	-	unary predicate which returns ​true for the elements expected to be found in the beginning of the range. The signature of the predicate function should be equivalent to the following: bool pred(const Type &a); The signature does not need to have const &, but the function must not modify the objects passed to it. The type Type must be such that an object of type InputIterator can be dereferenced and then implicitly converted to Type. ​

Return value

true if the range [first, last) is empty or is partitioned by p. false otherwise.

Complexity

At most std::distance(first, last) applications of p.

Possible implementation

template< class InputIterator, class UnaryPredicate > bool is_partitioned(InputIterator first, InputIterator last, UnaryPredicate p) { for (; first != last; ++first) if (!p(*first)) break; for (; first != last; ++first) if (p(*first)) return false; return true; }

Example

#include <algorithm>
#include <array>
#include <iostream>
 
int main()
{
    std::array<int, 9> v = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
 
    auto is_even = [](int i){ return i % 2 == 0; };
    std::cout.setf(std::ios_base::boolalpha);
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
    std::partition(v.begin(), v.end(), is_even);
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even) << ' ';
 
    std::reverse(v.begin(), v.end());
    std::cout << std::is_partitioned(v.begin(), v.end(), is_even);
}

Output:

false true false

See also

partition	divides a range of elements into two groups (function template)
partition_point (C++11)	locates the partition point of a partitioned range (function template)