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adjustable_priority_queue.h
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adjustable_priority_queue.h
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// Copyright 2010-2018 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef OR_TOOLS_BASE_ADJUSTABLE_PRIORITY_QUEUE_H_
#define OR_TOOLS_BASE_ADJUSTABLE_PRIORITY_QUEUE_H_
#include <stddef.h>
#include <functional>
#include <list>
#include <vector>
#include "ortools/base/basictypes.h"
#include "ortools/base/logging.h"
#include "ortools/base/macros.h"
template <typename T, typename Comparator>
class LowerPriorityThan {
public:
explicit LowerPriorityThan(Comparator* compare) : compare_(compare) {}
bool operator()(T* a, T* b) const { return (*compare_)(*a, *b); }
private:
Comparator* compare_;
};
template <typename T, typename Comp = std::less<T> >
class AdjustablePriorityQueue {
public:
// The objects references 'c' and 'm' are not required to be alive for the
// lifetime of this object.
AdjustablePriorityQueue() {}
AdjustablePriorityQueue(const Comp& c) : c_(c) {}
AdjustablePriorityQueue(const AdjustablePriorityQueue&) = delete;
AdjustablePriorityQueue& operator=(const AdjustablePriorityQueue&) = delete;
AdjustablePriorityQueue(AdjustablePriorityQueue&&) = default;
AdjustablePriorityQueue& operator=(AdjustablePriorityQueue&&) = default;
void Add(T* val) {
// Extend the size of the vector by one. We could just use
// vector<T>::resize(), but maybe T is not default-constructible.
elems_.push_back(val);
AdjustUpwards(elems_.size() - 1);
}
void Remove(T* val) {
int end = elems_.size() - 1;
int i = val->GetHeapIndex();
if (i == end) {
elems_.pop_back();
return;
}
elems_[i] = elems_[end];
elems_[i]->SetHeapIndex(i);
elems_.pop_back();
NoteChangedPriority(elems_[i]);
}
bool Contains(const T* val) const {
int i = val->GetHeapIndex();
return (i >= 0 && i < elems_.size() && elems_[i] == val);
}
void NoteChangedPriority(T* val) {
LowerPriorityThan<T, Comp> lower_priority(&c_);
int i = val->GetHeapIndex();
int parent = (i - 1) / 2;
if (lower_priority(elems_[parent], val)) {
AdjustUpwards(i);
} else {
AdjustDownwards(i);
}
}
// If val ever changes its priority, you need to call this function
// to notify the pq so it can move it in the heap accordingly.
T* Top() { return elems_[0]; }
const T* Top() const { return elems_[0]; }
void AllTop(std::vector<T*>* topvec) {
topvec->clear();
if (Size() == 0) return;
std::list<int> need_to_check_children;
need_to_check_children.push_back(0);
// Implements breadth-first search down tree, stopping whenever
// there's an element < top
while (!need_to_check_children.empty()) {
int ind = need_to_check_children.front();
need_to_check_children.pop_front();
topvec->push_back(elems_[ind]);
int leftchild = 1 + 2 * ind;
if (leftchild < Size()) {
if (!LowerPriorityThan<T, Comp>(&c_)(elems_[leftchild], elems_[ind])) {
need_to_check_children.push_back(leftchild);
}
int rightchild = leftchild + 1;
if (rightchild < Size() &&
!LowerPriorityThan<T, Comp>(&c_)(elems_[rightchild], elems_[ind])) {
need_to_check_children.push_back(rightchild);
}
}
}
}
// If there are ties for the top, this returns all of them.
void Pop() { Remove(Top()); }
int Size() const { return elems_.size(); }
// Returns the number of elements for which storage has been allocated.
int Capacity() const { return elems_.capacity(); }
// Allocates storage for a given number of elements.
void SetCapacity(size_t c) { elems_.reserve(c); }
bool IsEmpty() const { return elems_.empty(); }
void Clear() { elems_.clear(); }
// CHECKs that the heap is actually a heap (each "parent" of >=
// priority than its child).
void CheckValid() {
for (int i = 0; i < elems_.size(); ++i) {
int left_child = 1 + 2 * i;
if (left_child < elems_.size()) {
CHECK(
!(LowerPriorityThan<T, Comp>(&c_))(elems_[i], elems_[left_child]));
}
int right_child = left_child + 1;
if (right_child < elems_.size()) {
CHECK(
!(LowerPriorityThan<T, Comp>(&c_))(elems_[i], elems_[right_child]));
}
}
}
// This is for debugging, e.g. the caller can use it to
// examine the heap for rationality w.r.t. other parts of the
// program.
const std::vector<T*>* Raw() const { return &elems_; }
private:
void AdjustUpwards(int i) {
T* const t = elems_[i];
while (i > 0) {
const int parent = (i - 1) / 2;
if (!c_(*elems_[parent], *t)) {
break;
}
elems_[i] = elems_[parent];
elems_[i]->SetHeapIndex(i);
i = parent;
}
elems_[i] = t;
t->SetHeapIndex(i);
}
void AdjustDownwards(int i) {
T* const t = elems_[i];
while (true) {
const int left_child = 1 + 2 * i;
if (left_child >= elems_.size()) {
break;
}
const int right_child = left_child + 1;
const int next_i = (right_child < elems_.size() &&
c_(*elems_[left_child], *elems_[right_child]))
? right_child
: left_child;
if (!c_(*t, *elems_[next_i])) {
break;
}
elems_[i] = elems_[next_i];
elems_[i]->SetHeapIndex(i);
i = next_i;
}
elems_[i] = t;
t->SetHeapIndex(i);
}
Comp c_;
std::vector<T*> elems_;
};
#endif // OR_TOOLS_BASE_ADJUSTABLE_PRIORITY_QUEUE_H_