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//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2026
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#pragma once
#include "td/utils/common.h"
namespace td {
struct HeapNode {
bool in_heap() const {
return pos_ != -1;
}
bool is_top() const {
return pos_ == 0;
}
void remove() {
pos_ = -1;
}
int32 pos_ = -1;
};
template <class KeyT, int K = 4>
class KHeap {
public:
bool empty() const {
return array_.empty();
}
size_t size() const {
return array_.size();
}
KeyT top_key() const {
return array_[0].key_;
}
KeyT get_key(const HeapNode *node) const {
auto pos = static_cast<size_t>(node->pos_);
CHECK(pos < array_.size());
return array_[pos].key_;
}
const HeapNode *top() const {
return array_[0].node_;
}
HeapNode *pop() {
CHECK(!empty());
HeapNode *result = array_[0].node_;
result->remove();
erase(static_cast<size_t>(0));
return result;
}
void insert(KeyT key, HeapNode *node) {
CHECK(!node->in_heap());
array_.push_back({key, node});
fix_up(array_.size() - 1);
}
void fix(KeyT key, HeapNode *node) {
auto pos = static_cast<size_t>(node->pos_);
CHECK(pos < array_.size());
KeyT old_key = array_[pos].key_;
array_[pos].key_ = key;
if (key < old_key) {
fix_up(pos);
} else {
fix_down(pos);
}
}
void erase(HeapNode *node) {
auto pos = static_cast<size_t>(node->pos_);
node->remove();
CHECK(pos < array_.size());
erase(pos);
}
template <class F>
void for_each(F &&f) const {
for (auto &it : array_) {
f(it.key_, it.node_);
}
}
template <class F>
void for_each(F &&f) {
for (auto &it : array_) {
f(it.key_, it.node_);
}
}
void check() const {
for (size_t i = 0; i < array_.size(); i++) {
for (size_t j = i * K + 1; j < i * K + 1 + K && j < array_.size(); j++) {
CHECK(array_[i].key_ <= array_[j].key_);
}
}
}
private:
struct Item {
KeyT key_;
HeapNode *node_;
};
vector<Item> array_;
void fix_up(size_t pos) {
auto item = array_[pos];
while (pos) {
auto parent_pos = (pos - 1) / K;
auto parent_item = array_[parent_pos];
if (parent_item.key_ < item.key_) {
break;
}
parent_item.node_->pos_ = static_cast<int32>(pos);
array_[pos] = parent_item;
pos = parent_pos;
}
item.node_->pos_ = static_cast<int32>(pos);
array_[pos] = item;
}
void fix_down(size_t pos) {
auto item = array_[pos];
while (true) {
auto left_pos = pos * K + 1;
auto right_pos = min(left_pos + K, array_.size());
auto next_pos = pos;
KeyT next_key = item.key_;
for (auto i = left_pos; i < right_pos; i++) {
KeyT i_key = array_[i].key_;
if (i_key < next_key) {
next_key = i_key;
next_pos = i;
}
}
if (next_pos == pos) {
break;
}
array_[pos] = array_[next_pos];
array_[pos].node_->pos_ = static_cast<int32>(pos);
pos = next_pos;
}
item.node_->pos_ = static_cast<int32>(pos);
array_[pos] = item;
}
void erase(size_t pos) {
array_[pos] = array_.back();
array_.pop_back();
if (pos < array_.size()) {
fix_down(pos);
fix_up(pos);
}
if (array_.capacity() > 50 && array_.size() < array_.capacity() / 4) {
array_.shrink_to_fit();
}
}
};
} // namespace td
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