std::ranges::is_permutation

 

C++

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Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)   execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)    (C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
Numeric operations
iota (C++11) inner_product adjacent_difference    accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17)    exclusive_scan (C++17) transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

Constrained algorithms

All names in this menu belong to namespace std::ranges

Non-modifying sequence operations

all_ofany_ofnone_of for_each for_each_n    countcount_if adjacent_find mismatch equal lexicographical_compare    containscontains_subrange (C++23)(C++23) findfind_iffind_if_not find_lastfind_last_iffind_last_if_not (C++23)(C++23)(C++23)   find_end find_first_of search search_n starts_with (C++23) ends_with (C++23)

Modifying sequence operations

copycopy_if copy_n copy_backward    move move_backward shift_leftshift_right (C++23)(C++23)   fill fill_n generate generate_n    transform swap_ranges    shuffle sample removeremove_if replacereplace_if reverse rotate remove_copyremove_copy_if    unique replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy

Partitioning operations

is_partitioned    partition_point    partition    partition_copy    stable_partition

Sorting operations

is_sorted is_sorted_until     sort stable_sort         partial_sort       nth_element partial_sort_copy

Binary search operations (on sorted ranges)

lower_bound         upper_bound         binary_search      equal_range

Set operations (on sorted ranges)

merge inplace_merge       set_difference set_intersection    set_union          includes set_symmetric_difference

Heap operations

is_heap is_heap_until       make_heap           sort_heap push_heap pop_heap

Minimum/maximum operations

max max_element         min min_element         minmax minmax_element     clamp

Permutation operations

is_permutation      next_permutation    prev_permutation

Fold operations

fold_left (C++23) fold_left_first (C++23)   fold_right (C++23) fold_right_last (C++23)   fold_left_with_iter (C++23) fold_left_first_with_iter (C++23)

Numeric operations iota (C++23)             Random number generation generate_random (C++26)

Operations on uninitialized storage

construct_at    destroy destroy_n destroy_at uninitialized_copy    uninitialized_move uninitialized_fill uninitialized_copy_n    uninitialized_move_n uninitialized_fill_n uninitialized_default_construct uninitialized_default_construct_n uninitialized_value_construct uninitialized_value_construct_n

Return types

in_fun_result in_in_result in_found_result    in_out_result in_in_out_result    in_out_out_result    min_max_result out_value_result (C++23) in_value_result (C++23)

 

Defined in header <algorithm>
Call signature
template< std::forward_iterator I1, std::sentinel_for<I1> S1,           std::forward_iterator I2, std::sentinel_for<I2> S2,           class Proj1 = std::identity, class Proj2 = std::identity,           std::indirect_equivalence_relation<std::projected<I1, Proj1>,                                              std::projected<I2, Proj2>>                                                 Pred = ranges::equal_to > constexpr bool is_permutation( I1 first1, S1 last1, I2 first2, S2 last2,                                Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} );	(1)	(since C++20)
template< ranges::forward_range R1, ranges::forward_range R2,      class Proj1 = std::identity, class Proj2 = std::identity,      std::indirect_equivalence_relation<std::projected<ranges::iterator_t<R1>, Proj1>,                                         std::projected<ranges::iterator_t<R2>, Proj2>>                                             Pred = ranges::equal_to > constexpr bool is_permutation( R1&& r1, R2&& r2, Pred pred = {},                                Proj1 proj1 = {}, Proj2 proj2 = {} );	(2)	(since C++20)

1) Returns true if there exists a permutation of the elements in range [first1, last1) that makes the range equal to [first2, last2) (after application of corresponding projections Proj1, Proj2, and using the binary predicate Pred as a comparator). Otherwise returns false.

2) Same as (1), but uses r1 as the first source range and r2 as the second source range, as if using ranges::begin(r1) as first1, ranges::end(r1) as last1, ranges::begin(r2) as first2, and ranges::end(r2) as last2.

The function-like entities described on this page are niebloids, that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

Parameters

first1, last1	-	the first range of the elements
first2, last2	-	the second range of the elements
r1	-	the first range of the elements
r2	-	the second range of the elements
pred	-	predicate to apply to the projected elements
proj1	-	projection to apply to the elements in the first range
proj2	-	projection to apply to the elements in the second range

Return value

true if the range [first1, last1) is a permutation of the range [first2, last2).

Complexity

At most \(\scriptsize \mathcal{O}(N^2)\)O(N²) applications of the predicate and each projection, or exactly \(\scriptsize N\)N if the sequences are already equal, where \(\scriptsize N\)N is ranges::distance(first1, last1). However if ranges::distance(first1, last1) != ranges::distance(first2, last2), no applications of the predicate and projections are made.

Notes

The permutation relation is an equivalence relation.

The ranges::is_permutation can be used in testing, namely to check the correctness of rearranging algorithms (e.g. sorting, shuffling, partitioning). If x is an original range and y is a permuted range then ranges::is_permutation(x, y) == true means that y consist of "the same" elements, maybe staying at other positions.

Possible implementation

struct is_permutation_fn { template< std::forward_iterator I1, std::sentinel_for<I1> S1, std::forward_iterator I2, std::sentinel_for<I2> S2, class Proj1 = std::identity, class Proj2 = std::identity, std::indirect_equivalence_relation<std::projected<I1, Proj1>, std::projected<I2, Proj2>> Pred = ranges::equal_to > constexpr bool operator()( I1 first1, S1 last1, I2 first2, S2 last2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ) const { // skip common prefix auto ret = std::ranges::mismatch(first1, last1, first2, last2, std::ref(pred), std::ref(proj1), std::ref(proj2)); first1 = ret.in1, first2 = ret.in2;   // iterate over the rest, counting how many times each element // from [first1, last1) appears in [first2, last2) for (auto i{ first1 }; i != last1; ++i) { const auto i_proj{ std::invoke(proj1, *i) }; auto i_cmp = [&]<typename T>(T&& t) { return std::invoke(pred, i_proj, std::forward<T>(t)); };   if (i != ranges::find_if(first1, i, i_cmp, proj1)) continue; // this *i has been checked   if (const auto m{ ranges::count_if(first2, last2, i_cmp, proj2) }; m == 0 or m != ranges::count_if(i, last1, i_cmp, proj1)) return false; } return true; }   template< ranges::forward_range R1, ranges::forward_range R2, class Proj1 = std::identity, class Proj2 = std::identity, std::indirect_equivalence_relation<std::projected<ranges::iterator_t<R1>, Proj1>, std::projected<ranges::iterator_t<R2>, Proj2>> Pred = ranges::equal_to > constexpr bool operator()( R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {} ) const { return (*this)(ranges::begin(r1), ranges::end(r1), ranges::begin(r2), ranges::end(r2), std::move(pred), std::move(proj1), std::move(proj2)); } };   inline constexpr is_permutation_fn is_permutation{};

Example

Run this code

#include <algorithm>
#include <array>
#include <cmath>
#include <iostream>
#include <ranges>
 
auto& operator<< (auto& os, std::ranges::forward_range auto const& v) {
    os << "{ ";
    for (auto const& e : v) os << e << ' ';
    return os << "}";
}
 
int main()
{
    static constexpr auto r1 = {1,2,3,4,5};
    static constexpr auto r2 = {3,5,4,1,2};
    static constexpr auto r3 = {3,5,4,1,1};
 
    static_assert(
        std::ranges::is_permutation(r1, r1) &&
        std::ranges::is_permutation(r1, r2) &&
        std::ranges::is_permutation(r2, r1) &&
        std::ranges::is_permutation(r1.begin(), r1.end(), r2.begin(), r2.end())
        );
 
    std::cout
        << std::boolalpha
        << "is_permutation( " << r1 << ", " << r2 << " ): "
        << std::ranges::is_permutation(r1, r2) << '\n'
        << "is_permutation( " << r1 << ", " << r3 << " ): "
        << std::ranges::is_permutation(r1, r3) << '\n'
 
        << "is_permutation with custom predicate and projections: "
        << std::ranges::is_permutation(
            std::array{ -14, -11, -13, -15, -12 },  // 1st range
            std::array{ 'F', 'E', 'C', 'B', 'D' },  // 2nd range
            [](int x, int y) { return abs(x) == abs(y); }, // predicate
            [](int x) { return x + 10; },           // projection for 1st range
            [](char y) { return int(y - 'A'); })    // projection for 2nd range
        << '\n';
}

Output:

is_permutation( { 1 2 3 4 5 }, { 3 5 4 1 2 } ): true
is_permutation( { 1 2 3 4 5 }, { 3 5 4 1 1 } ): false
is_permutation with custom predicate and projections: true

See also

ranges::next_permutation (C++20)	generates the next greater lexicographic permutation of a range of elements (niebloid)
ranges::prev_permutation (C++20)	generates the next smaller lexicographic permutation of a range of elements (niebloid)
is_permutation (C++11)	determines if a sequence is a permutation of another sequence (function template)
next_permutation	generates the next greater lexicographic permutation of a range of elements (function template)
prev_permutation	generates the next smaller lexicographic permutation of a range of elements (function template)
equivalence_relation (C++20)	specifies that a relation imposes an equivalence relation (concept)