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** Copyright (C) 2015 Corentin Chary <corentin.chary@gmail.cm>
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****************************************************************************/

#ifndef QPRIORITY_QUEUE_H
#define QPRIORITY_QUEUE_H

#include <QtCore/qalgorithms.h>

QT_BEGIN_HEADER

QT_BEGIN_NAMESPACE

QT_MODULE(Core)

template <class T> class QList;

#ifndef QT_NO_STL
#include <queue>
#include <vector>
#else
/* Fallback class used when stl is not available */
template <class T, typename LessThan = qLess < T > >
class QPriorityQueuePrivate {
public:
    inline QPriorityQueuePrivate(LessThan l) : lessThan(l), d() {}
    inline ~QPriorityQueuePrivate() {}

    inline void clear() { return d.clear(); }
    inline int size() const { return d.size(); }
    inline bool empty() const { return d.empty(); }

    inline T &top() { return d.front(); }

    void pop();
    void push(const T &value);
private:
    inline int parent(int i) {
    return (i - 1) / 2;
    }
    inline int leftChild(int i) {
    return 2 * i + 1;
    }
    inline int rightChild(int i) {
    return 2 * i + 2;
    }

    LessThan lessThan;
    QList < T > d;
};
#endif

template <class T, typename LessThan = qLess < T > >
class Q_CORE_EXPORT QPriorityQueue
{
public:
    inline QPriorityQueue(LessThan l = qLess < T >())
      : lessThan(l), d(lessThan) { }
    inline QPriorityQueue(const QPriorityQueue<T> &q)
      : lessThan(q.lessThan), d(q.d) { }
    inline ~QPriorityQueue() { }

    QPriorityQueue<T> &operator=(const QPriorityQueue<T> &q) {
      d = q.d; return *this;
    }

    inline int size() const { return d.size(); }
    inline bool isEmpty() const { return empty(); }

    // like qlist
    void clear();
    void append(const T &t) { return enqueue(t); }
    void append(const QList<T> &t);
    T takeFirst() { return dequeue(); }
    inline int length() const { return size(); } // Same as count()
    inline T& first() { return head(); }
    inline const T& first() const { return head(); }
    inline void removeFirst() { pop(); }
    inline bool startsWith(const T &t) const
    { return !isEmpty() && first() == t; }

    // like qqueue
    inline void enqueue(const T &t) { push(t); }
    inline T dequeue() { T t = d.top();	d.pop(); return t; }
    inline T &head() { return const_cast<T&>(top()); }
    inline const T &head() const { return top(); }

    // stl compatibility
    typedef int size_type;
    typedef T value_type;

    inline bool empty() const { return d.empty(); }
    inline const value_type& top() { Q_ASSERT(!isEmpty()); return d.top(); }
    inline void push(const value_type& x) { return d.push(x); }
    inline void pop() { Q_ASSERT(!isEmpty()); d.pop(); }

    // comfort
    inline QPriorityQueue<T> &operator+=(const T &t) {
      enqueue(t); return *this;
    }
    inline QPriorityQueue<T> &operator<< (const T &t) {
      enqueue(t); return *this;
    }
    inline QPriorityQueue<T> &operator>> (T &t) {
      t = d.top(); d.pop(); return *this;
    }

#ifndef QT_NO_STL
    static inline QPriorityQueue<T>fromStdPriorityQueue(
        const std::priority_queue<T> &q) {
      QPriorityQueue<T> tmp; tmp.d = q; return tmp;
    }
    inline std::priority_queue<T> toStdPriorityQueue() const {
      return d;
    }
#endif

private:
    LessThan lessThan;
#ifndef QT_NO_STL
    std::priority_queue <T, std::vector < T >, LessThan> d;
#else
    QPriorityQueuePrivate <T> d;
#endif
};

#ifndef QT_NO_STL

template <typename T, typename LessThan>
Q_INLINE_TEMPLATE void QPriorityQueue<T, LessThan>::clear()
{
    d = std::priority_queue <T, std::vector < T >, LessThan>(lessThan);
    //d = std::priority_queue<T>(lessThan);
}

#else

template <typename T, typename LessThan>
Q_INLINE_TEMPLATE void QPriorityQueue<T, LessThan>::clear()
{
    d.clear();
}

#endif

template <typename T, typename LessThan>
Q_OUTOFLINE_TEMPLATE void QPriorityQueue<T, LessThan>::append(const QList<T> &t)
{
    foreach (T & e, t)
    push(e);
}

// Re-implement std::priority_queue if STL not available, probably
// less efficient.
#ifdef QT_NO_STL
/*!
 *  Pop an element from the queue and reorder it using an
 *  inlined binary heap.
 *
 *  \internal
 */
template <typename T, typename LessThan>
Q_OUTOFLINE_TEMPLATE void QPriorityQueuePrivate<T, LessThan>::pop()
{
    int i = 0;
    ssize_t size = d.size();;

    if(!size)
    return;
    if(size == 1)
    return d.clear();

    d[0] = d.takeLast();

    while(i < size - 1) {
    int left = leftChild(i);
    int right = rightChild(i);
    bool validLeft = left < size;
    bool validRight = right < size;

    if(validLeft && lessThan(d.at(i), d.at(left)))
        if(validRight && !lessThan(d.at(right), d.at(left))) {
        d.swap(i, right);
        i = right;
        } else {
        d.swap(i, left);
        i = left;
        }
    else if(validRight && lessThan(d.at(i), d.at(right))) {
        d.swap(i, right);
        i = right;
    }
    else
        break;
    }
}

/*!
 *  Push an element with a given priority to the right place.
 *
 *  \internal
 */
template <typename T, typename LessThan>
Q_OUTOFLINE_TEMPLATE void QPriorityQueuePrivate<T, LessThan>::push(const T &value)
{
    int i = d.size();
    d.append(value);
    while(i != 0 && !lessThan(d.at(i), d.at(parent(i)))) {
    d.swap(i, parent(i));
    i = parent(i);
    }
}
#endif

QT_END_NAMESPACE

QT_END_HEADER

#endif // QPRIORITY_QUEUE_H