1//===- llvm/ADT/PriorityQueue.h - Priority queues ---------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8///
9/// \file
10/// This file defines the PriorityQueue class.
11///
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ADT_PRIORITYQUEUE_H
15#define LLVM_ADT_PRIORITYQUEUE_H
16
17#include <algorithm>
18#include <queue>
19
20namespace llvm {
21
22/// PriorityQueue - This class behaves like std::priority_queue and
23/// provides a few additional convenience functions.
24///
25template<class T,
26         class Sequence = std::vector<T>,
27         class Compare = std::less<typename Sequence::value_type> >
28class PriorityQueue : public std::priority_queue<T, Sequence, Compare> {
29public:
30  explicit PriorityQueue(const Compare &compare = Compare(),
31                         const Sequence &sequence = Sequence())
32    : std::priority_queue<T, Sequence, Compare>(compare, sequence)
33  {}
34
35  template<class Iterator>
36  PriorityQueue(Iterator begin, Iterator end,
37                const Compare &compare = Compare(),
38                const Sequence &sequence = Sequence())
39    : std::priority_queue<T, Sequence, Compare>(begin, end, compare, sequence)
40  {}
41
42  /// erase_one - Erase one element from the queue, regardless of its
43  /// position. This operation performs a linear search to find an element
44  /// equal to t, but then uses all logarithmic-time algorithms to do
45  /// the erase operation.
46  ///
47  void erase_one(const T &t) {
48    // Linear-search to find the element.
49    typename Sequence::size_type i = find(this->c, t) - this->c.begin();
50
51    // Logarithmic-time heap bubble-up.
52    while (i != 0) {
53      typename Sequence::size_type parent = (i - 1) / 2;
54      this->c[i] = this->c[parent];
55      i = parent;
56    }
57
58    // The element we want to remove is now at the root, so we can use
59    // priority_queue's plain pop to remove it.
60    this->pop();
61  }
62
63  /// reheapify - If an element in the queue has changed in a way that
64  /// affects its standing in the comparison function, the queue's
65  /// internal state becomes invalid. Calling reheapify() resets the
66  /// queue's state, making it valid again. This operation has time
67  /// complexity proportional to the number of elements in the queue,
68  /// so don't plan to use it a lot.
69  ///
70  void reheapify() {
71    std::make_heap(this->c.begin(), this->c.end(), this->comp);
72  }
73
74  /// clear - Erase all elements from the queue.
75  ///
76  void clear() {
77    this->c.clear();
78  }
79};
80
81} // End llvm namespace
82
83#endif
84