PriorityQueue.h

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//===- llvm/ADT/PriorityQueue.h - Priority queues ---------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the PriorityQueue class.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_PRIORITYQUEUE_H
#define LLVM_ADT_PRIORITYQUEUE_H

#include <algorithm>
#include <queue>

namespace llvm {

/// PriorityQueue - This class behaves like std::priority_queue and
/// provides a few additional convenience functions.
///
template<class T,
         class Sequence = std::vector<T>,
         class Compare = std::less<typename Sequence::value_type> >
class PriorityQueue : public std::priority_queue<T, Sequence, Compare> {
public:
  explicit PriorityQueue(const Compare &compare = Compare(),
                         const Sequence &sequence = Sequence())
    : std::priority_queue<T, Sequence, Compare>(compare, sequence)
  {}

  template<class Iterator>
  PriorityQueue(Iterator begin, Iterator end,
                const Compare &compare = Compare(),
                const Sequence &sequence = Sequence())
    : std::priority_queue<T, Sequence, Compare>(begin, end, compare, sequence)
  {}

  /// erase_one - Erase one element from the queue, regardless of its
  /// position. This operation performs a linear search to find an element
  /// equal to t, but then uses all logarithmic-time algorithms to do
  /// the erase operation.
  ///
  void erase_one(const T &t) {
    // Linear-search to find the element.
    typename Sequence::size_type i = find(this->c, t) - this->c.begin();

    // Logarithmic-time heap bubble-up.
    while (i != 0) {
      typename Sequence::size_type parent = (i - 1) / 2;
      this->c[i] = this->c[parent];
      i = parent;
    }

    // The element we want to remove is now at the root, so we can use
    // priority_queue's plain pop to remove it.
    this->pop();
  }

  /// reheapify - If an element in the queue has changed in a way that
  /// affects its standing in the comparison function, the queue's
  /// internal state becomes invalid. Calling reheapify() resets the
  /// queue's state, making it valid again. This operation has time
  /// complexity proportional to the number of elements in the queue,
  /// so don't plan to use it a lot.
  ///
  void reheapify() {
    std::make_heap(this->c.begin(), this->c.end(), this->comp);
  }

  /// clear - Erase all elements from the queue.
  ///
  void clear() {
    this->c.clear();
  }
};

} // End llvm namespace

#endif