STL 之 queue、priority_queue 源代码剖析

最新推荐文章于 2024-08-14 09:42:16 发布

转载最新推荐文章于 2024-08-14 09:42:16 发布 · 128 阅读

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本文详细介绍了STL中的队列(queue)和优先队列(priority_queue)的实现原理与使用方法。探讨了队列如何通过底层容器实现先进先出(FIFO)的数据操作，并分析了优先队列如何借助堆数据结构实现高效的插入与删除最大(或最小)元素的功能。

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/*
* Copyright (c) 1994
* Hewlett-Packard Company
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Hewlett-Packard Company makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*
*
* Copyright (c) 1996,1997
* Silicon Graphics Computer Systems, Inc.
*
* Permission to use, copy, modify, distribute and sell this software
* and its documentation for any purpose is hereby granted without fee,
* provided that the above copyright notice appear in all copies and
* that both that copyright notice and this permission notice appear
* in supporting documentation. Silicon Graphics makes no
* representations about the suitability of this software for any
* purpose. It is provided "as is" without express or implied warranty.
*/
/* NOTE: This is an internal header file, included by other STL headers.
* You should not attempt to use it directly.
*/
#ifndef __SGI_STL_INTERNAL_QUEUE_H
#define __SGI_STL_INTERNAL_QUEUE_H
__STL_BEGIN_NAMESPACE
#ifndef __STL_LIMITED_DEFAULT_TEMPLATES
template <class T, class Sequence = deque<T> >
#else
template <class T, class Sequence>
#endif
class queue {
friend bool operator== __STL_NULL_TMPL_ARGS (const queue& x, const queue& y);
friend bool operator< __STL_NULL_TMPL_ARGS (const queue& x, const queue& y);
public:
typedef typename Sequence::value_type value_type;
typedef typename Sequence::size_type size_type;
typedef typename Sequence::reference reference;
typedef typename Sequence::const_reference const_reference;
protected:
Sequence c; // 底層容器
public:
// 下面全然利用 Sequence c 的操作。完毕 queue 的操作。
bool empty() const { return c.empty(); }
size_type size() const { return c.size(); }
reference front() { return c.front(); }
const_reference front() const { return c.front(); }
reference back() { return c.back(); }
const_reference back() const { return c.back(); }
// deque 是兩頭可進出，queue 是末端進，前端出（所以先進者先出）。

void push(const value_type& x) { c.push_back(x); } void pop() { c.pop_front(); } }; template <class T, class Sequence> bool operator==(const queue<T, Sequence>& x, const queue<T, Sequence>& y) { return x.c == y.c; } template <class T, class Sequence> bool operator<(const queue<T, Sequence>& x, const queue<T, Sequence>& y) { return x.c < y.c; } #ifndef __STL_LIMITED_DEFAULT_TEMPLATES /* 預設情況下 priority_queue 係利用 vector 完毕一個 max-heap，後者乃為一個以 array（或 vector）表現的二元樹。其條件是，必須為全然樹（complete tree，此為結構特性），且每個節點值都大於或等於其任一子節點值（此為次序特性）。因此根節點為最大值。Max-heap 適用於 priority_queue 所需特性。

*/ template <class T, class Sequence = vector<T>, class Compare = less<typename Sequence::value_type> > #else template <class T, class Sequence, class Compare> #endif class priority_queue { public: typedef typename Sequence::value_type value_type; typedef typename Sequence::size_type size_type; typedef typename Sequence::reference reference; typedef typename Sequence::const_reference const_reference; protected: Sequence c; // 底層容器 Compare comp; // 元素大小比较標準 public: priority_queue() : c() {} explicit priority_queue(const Compare& x) : c(), comp(x) {} // 下面用到的make_heap(), push_heap(), pop_heap()都是泛型演算法 // 注意，任一個建構式都立马於底層容器內產生一個implicit representation heap。

#ifdef __STL_MEMBER_TEMPLATES template <class InputIterator> priority_queue(InputIterator first, InputIterator last, const Compare& x) : c(first, last), comp(x) { make_heap(c.begin(), c.end(), comp); } template <class InputIterator> priority_queue(InputIterator first, InputIterator last) : c(first, last) { make_heap(c.begin(), c.end(), comp); } #else /* __STL_MEMBER_TEMPLATES */ priority_queue(const value_type* first, const value_type* last, const Compare& x) : c(first, last), comp(x) { make_heap(c.begin(), c.end(), comp); } priority_queue(const value_type* first, const value_type* last) : c(first, last) { make_heap(c.begin(), c.end(), comp); } #endif /* __STL_MEMBER_TEMPLATES */ bool empty() const { return c.empty(); } size_type size() const { return c.size(); } const_reference top() const { return c.front(); } void push(const value_type& x) { __STL_TRY { // push_heap 是泛型演算法。先利用底層容器的 push_back() 將新元素 // 推入末端。再重排 heap。見C++ Primer p.1195。

c.push_back(x); push_heap(c.begin(), c.end(), comp); // push_heap 是泛型演算法 } __STL_UNWIND(c.clear()); } void pop() { __STL_TRY { // pop_heap 是泛型演算法，從 heap 內取出一個元素。它並不是真正將元素 // 彈出。而是重排 heap，然後再以底層容器的 pop_back() 取得被彈出 // 的元素。

見C++ Primer p.1195。

pop_heap(c.begin(), c.end(), comp); c.pop_back(); } __STL_UNWIND(c.clear()); } }; // no equality is provided __STL_END_NAMESPACE #endif /* __SGI_STL_INTERNAL_QUEUE_H */ // Local Variables: // mode:C++ // End: