std::is_sorted_until

 

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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
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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
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is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
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is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
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lower_bound upper_bound	binary_search equal_range
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is_heap is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
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C library
qsort	bsearch

 

Defined in header <algorithm>
template< class ForwardIterator > ForwardIterator is_sorted_until( ForwardIterator first, ForwardIterator last );	(1)	(since C++11)
template< class ForwardIterator, class Compare > ForwardIterator is_sorted_until( ForwardIterator first, ForwardIterator last,                                  Compare comp );	(2)	(since C++11)

Examines the range [first, last) and finds the largest range beginning at first in which the elements are sorted in ascending order. The first version of the function uses operator< to compare the elements, the second uses the given comparison function comp.

Parameters

first, last	-	the range of elements to examine
comp	-	comparison function which returns ​true if the first argument is less than the second. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1 &a, const Type2 &b); The signature does not need to have const &, but the function must not modify the objects passed to it. The types  Type1 and  Type2 must be such that an object of type ForwardIterator can be dereferenced and then implicitly converted to both of them. ​

Return value

The upper bound of the largest range beginning at first in which the elements are sorted in ascending order. That is, the last iterator it for which range [first, it) is sorted.

Complexity

linear in the distance between first and last

Possible implementation

First version
template<class ForwardIterator> ForwardIterator is_sorted_until(ForwardIterator first, ForwardIterator last) { if (first != last) { ForwardIterator next = first; while (++next != last) { if (*next < *first) return next; first = next; } } return last; }
Second version
template< class ForwardIterator, class Compare > ForwardIterator is_sorted_until(ForwardIterator first, ForwardIterator last, Compare comp) { if (first != last) { ForwardIterator next = first; while (++next != last) { if (comp(*next, *first)) return next; first = next; } } return last;

Example

#include <iostream>
#include <algorithm>
#include <iterator>
#include <random>
 
int main()
{
    std::random_device rd;
    std::mt19937 g(rd());
    const int N = 6;
    int nums[N] = {3, 1, 4, 1, 5, 9};
 
    const int min_sorted_size = 4;
    int sorted_size = 0;
    do {
        std::random_shuffle(nums, nums + N, g);
        int *sorted_end = std::is_sorted_until(nums, nums + N);
        sorted_size = std::distance(nums, sorted_end);
 
        for (auto i : nums) std::cout << i << ' ';
        std::cout << " : " << sorted_size << " initial sorted elements\n";
    } while (sorted_size < min_sorted_size);
}

Possible output:

4 1 9 5 1 3  : 1 initial sorted elements
4 5 9 3 1 1  : 3 initial sorted elements
9 3 1 4 5 1  : 1 initial sorted elements
1 3 5 4 1 9  : 3 initial sorted elements
5 9 1 1 3 4  : 2 initial sorted elements
4 9 1 5 1 3  : 2 initial sorted elements
1 1 4 9 5 3  : 4 initial sorted elements

See also

is_sorted (C++11)	checks whether a range is sorted into ascending order (function template)