namespace std {
template <class RandomAccessIterator>
void make_heap(RandomAccessIterator first,
RandomAccessIterator last); // (1) C++03
template <class RandomAccessIterator>
constexpr void make_heap(RandomAccessIterator first,
RandomAccessIterator last); // (1) C++20
template <class RandomAccessIterator, class Compare>
void make_heap(RandomAccessIterator first,
RandomAccessIterator last,
Compare comp); // (2) C++03
template <class RandomAccessIterator, class Compare>
constexpr void make_heap(RandomAccessIterator first,
RandomAccessIterator last,
Compare comp); // (2) C++20
}
概要
イテレータ範囲[first, last)をヒープ化する。
テンプレートパラメータ制約
*firstの型はMoveConstructibleとMoveAssignableの要件を満たしていること
効果
[first,last) の範囲で heap を構築する
戻り値
なし
計算量
最大で 3 * (last - first) 回比較する
例
#include <iostream>
#include <vector>
#include <algorithm>
int main()
{
std::vector<int> v = {3, 1, 4};
// ヒープ化する
std::make_heap(v.begin(), v.end());
std::for_each(v.begin(), v.end(), [](int x) {
std::cout << x << std::endl;
});
}
出力
4
1
3
実装例
template <class RandomAccessIterator>
void make_heap(RandomAccessIterator first, RandomAccessIterator last)
{
using difference_type = typename std::iterator_traits<RandomAccessIterator>::difference_type;
using value_type = typename std::iterator_traits<RandomAccessIterator>::value_type;
const difference_type len = last - first;
for (difference_type top = len / 2 - 1; top >= 0; --top) {
value_type v = std::move(first[top]);
difference_type p = top;
for (c = p * 2 + 1; c < len; c = p * 2 + 1) {
if (c + 1 < len && first[c] < first[c + 1])
++c;
if (!bool(v < first[c]))
break;
first[p] = std::move(first[c]);
p = c;
}
first[p] = std::move(v);
}
}
template <class RandomAccessIterator, class Compare>
void make_heap(RandomAccessIterator first, RandomAccessIterator last, Compare comp)
{
using difference_type = typename std::iterator_traits<RandomAccessIterator>::difference_type;
using value_type = typename std::iterator_traits<RandomAccessIterator>::value_type;
const difference_type len = last - first;
for (difference_type top = len / 2 - 1; top >= 0; --top) {
value_type v = std::move(first[top]);
difference_type p = top;
for (c = p * 2 + 1; c < len; c = p * 2 + 1) {
if (c + 1 < len && comp(first[c], first[c + 1]))
++c;
if (!bool(comp(v, first[c])))
break;
first[p] = std::move(first[c]);
p = c;
}
first[p] = std::move(v);
}
}
なお、push_heap を使用すると以下のように実装できるが、一般的に上記の実装方法の方が効率が良いようである。
template <class RandomAccessIterator>
void make_heap(RandomAccessIterator first, RandomAccessIterator last)
{
for (RandomAccessIterator current = first + 1; current < last; ) {
std::push_heap(first, ++current);
}
}
template <class RandomAccessIterator, class Compare>
void make_heap(RandomAccessIterator first, RandomAccessIterator last, Compare comp)
{
for (RandomAccessIterator current = first + 1; current < last; ) {
std::push_heap(first, ++current, comp);
}
}