std::partial_sort

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Defined in header <algorithm>

template< class RandomAccessIterator >

void partial_sort( RandomAccessIterator first,
                   RandomAccessIterator middle,

                   RandomAccessIterator last );
(1)
template< class RandomAccessIterator, class Compare >

void partial_sort( RandomAccessIterator first,
                   RandomAccessIterator middle,

                   RandomAccessIterator last, Compare comp );
(2)

Sorts some of the elements in the range [first, last) in ascending order. The first middle - first of these elements are placed in the range [first, middle). The order of equal elements is guaranteed to be preserved. The order of the remaining elements in the range [middle, last) is unspecified. The first version uses operator< to compare the elements, the second version uses the given comparison function comp.

Contents

[edit] Parameters

first, last - the range of elements to sort
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 RandomAccessIterator can be dereferenced and then implicitly converted to both of them. ​

[edit] Return value

(none)

[edit] Complexity

O(N·log2(N)), where N = std::distance(first, last) applications of cmp. If additional memory is available, then the complexity is O(N·log(N))

[edit] Example

#include <algorithm>
#include <functional>
#include <array>
#include <iostream>
 
int main()
{
    std::array<int, 10> s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
 
    std::partial_sort(s.begin(), s.begin() + 3, s.end());
    for (int a : s) {
        std::cout << a << " ";
    } 
}

Output:

0 1 2 7 8 6 5 9 4 3

[edit] See also

partial_sort_copy
copies and partially sorts a range of elements
(function template)
stable_sort
sorts a range of elements while preserving order between equal elements
(function template)
sort
sorts a range into ascending order
(function template)