# std::sort_heap

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< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class RandomIt > void sort_heap( RandomIt first, RandomIt last ); | (1) |
template< class RandomIt, class Compare > void sort_heap( RandomIt first, RandomIt last, Compare comp ); | (2) |

Converts the max heap `[first, last)` into a sorted range in ascending order. The resulting range no longer has the heap property.

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 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

(none)

### Complexity

At most N×log(N) comparisons where N=std::distance(first, last).

### Notes

A max heap is a range of elements `[f,l)` that has the following properties:

  - With `N = l - f`, for all `0 < i < N`, `f[floor(

    i-1
    2

    )]` does not compare less than `f[i]`.
  - a new element can be added using std::push_heap()
  - the first element can be removed using std::pop_heap()

### Possible implementation

First version

    template< class RandomIt >
    void sort_heap( RandomIt first, RandomIt last );
    {
        while (first != last)
            std::pop_heap(first, last--);
    }

Second version

    template< class RandomIt, class Compare >
    void sort_heap( RandomIt first, RandomIt last, Compare comp );
    {
        while (first != last)
            std::pop_heap(first, last--, comp);
    }

### Example

Run this code

    #include <algorithm>
    #include <vector>
    #include <iostream>

    int main()
    {
        std::vector<int> v = {3, 1, 4, 1, 5, 9};

        std::make_heap(v.begin(), v.end());

        std::cout << "heap:\t";
        for (const auto &i : v) {
            std::cout << i << ' ';
        }

        std::sort_heap(v.begin(), v.end());

        std::cout << "\nsorted:\t";
        for (const auto &i : v) {
            std::cout << i << ' ';
        }
        std::cout << '\n';
    }

Output:

    heap:   9 4 5 1 1 3
    sorted: 1 1 3 4 5 9

### See also

make_heap | creates a max heap out of a range of elements (function template)

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