< cpp‎ | algorithm
Revision as of 11:02, 9 November 2012 by (Talk)

Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations

Numeric operations
C library

Template:ddcl list begin <tr class="t-dsc-header">

Defined in header <algorithm>

<td></td> <td></td> </tr> <tr class="t-dcl ">

<td >
template< class RandomIt >
void partial_sort( RandomIt first, RandomIt middle, RandomIt last );

<td > (1) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl ">

<td >
template< class RandomIt, class Compare >
void partial_sort( RandomIt first, RandomIt middle, RandomIt last, Compare comp );

<td > (2) </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end

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 not 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.



first, last - the range of elements to sort
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) 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 object must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type RandomIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
RandomIt must meet the requirements of ValueSwappable and RandomAccessIterator.
The type of dereferenced RandomIt must meet the requirements of MoveAssignable and MoveConstructible.

Return value



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))


#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 << " ";


0 1 2 7 8 6 5 9 4 3

See also

Template:cpp/algorithm/dcl list nth elementTemplate:cpp/algorithm/dcl list partial sort copyTemplate:cpp/algorithm/dcl list stable sortTemplate:cpp/algorithm/dcl list sort