C++中字符串优先级队列的未排序双向链表

Question

我正在尝试使用未排序的双向链表实现字符串的“优先级”队列，但我完全停留在 dequeue 方法上（在代码的底部/之前可能存在问题）。优先级队列是指第一个要出队的元素是最小元素的队列。

您介意看看我的代码，并给我一些提示，说明我哪里错了吗？

非常感谢您的帮助。

马特

/*************************************************************
 * File: pqueue-doublylinkedlist.cpp
 *
 * Implementation file for the DoublyLinkedListPriorityQueue
 * class.
 */

#include "pqueue-doublylinkedlist.h"
#include "error.h"

/* Implementation notes: DoublyLinkedListPriorityQueue constructor
 * ----------------------------------------------------------------
 * This function initializes an empty priority queue represented as a doubly 
 * linked-list.
 */

DoublyLinkedListPriorityQueue::DoublyLinkedListPriorityQueue() {
    listHead = new Cell;
    listHead = NULL;
    count = 0;
}

/* Implementation notes: DoublyLinkedListPriorityQueue destructor
 * --------------------------------------------------------------
 * This function deletes every cell in the priority queue.
 */

DoublyLinkedListPriorityQueue::~DoublyLinkedListPriorityQueue() {
    Cell *temp, *link;
    temp = link = new Cell;

    temp = listHead;
    while (temp != NULL) {
        link = temp->next;
        delete temp;
        temp = link;
    }
    count = 0;
}

/* Implementation notes: DoublyLinkedListPriorityQueue size
 * --------------------------------------------------------
 * Returns the size of the priority queue.
 */

int DoublyLinkedListPriorityQueue::size() {
    return count;
}

/* Implementation notes: DoublyLinkedListPriorityQueue isEmpty
 * -----------------------------------------------------------
 * Returns true if there is no cell within the list.
 */

bool DoublyLinkedListPriorityQueue::isEmpty() {
    return (count == 0);
}

/* Implementation notes: DoublyLinkedListPriorityQueue enqueue
 * -----------------------------------------------------------
 * Enqueues the new Cell into the chain just after the head Cell.
 */

void DoublyLinkedListPriorityQueue::enqueue(string value) {

    Cell *newOne = new Cell;
    newOne->str = value;
    newOne->prev = NULL;

    newOne->next = listHead;
    listHead = newOne;

    count++;
}

/* Implementation notes: DoublyLinkedListPriorityQueue peek
 * --------------------------------------------------------
 * Returns the string value of the next node to be dequeued.
 */

string DoublyLinkedListPriorityQueue::peek() {
    if (isEmpty()) error("peek an empty list");

    curr = new Cell;

    curr = listHead;
    string result = listHead->str;

    for (curr = listHead; curr != NULL; curr = curr->next) {
        if (curr->str != "" && curr->str < result) {
            result = curr->str;
        }
    }

    return result;
}

/* Implementation notes: DoublyLinkedListPriorityQueue dequeueMin
 * --------------------------------------------------------------
 * Deletes the node with the smallest string and returns this string value.
 */

string DoublyLinkedListPriorityQueue::dequeueMin() {
    if (isEmpty()) error("dequeueMin an empty list");

    Cell *temp;
    temp = curr = new Cell;
    temp = curr = NULL;

    string result = listHead->str;

    // find the node to delete and store a pointer on it
    for (curr = listHead; curr != NULL; curr = curr->next) {
        if (curr->str != "" && curr->str < result) {
            result = curr->str;
            temp = curr;
        }
    }

    // first position (if: node to delete prev == NULL)
    if (temp->prev == NULL) {
        temp = listHead->next;
        delete listHead;
        listHead = temp;

    // delete from last position (else if: node to delete next == NULL)
    } else if (temp->next == NULL) {
        curr = temp->prev;
        curr->next = NULL;
        delete temp;

    // other position (else)
    } else {
        temp->prev->next = temp->next;
        temp->next->prev = temp->prev;
        delete temp;
    }

    count--;

    return result;
}

Answer 1

将优先级队列实现为双向链表（或者实际上，实现一个）是非常不寻常的，因为有一个 STL 实现可供使用：

#include <iostream>
#include <queue>
#include <functional>

int main(void) {
    std::priority_queue<std::string, std::vector<std::string>,
            std::greater<std::string> > pq;

    pq.push("foo");
    pq.push("bar");
    pq.push("quux");

    while( !pq.empty() ) {
        std::cout << pq.top() << std::endl;
        pq.pop();
    }

    return 0;
}

我发布此内容的假设是，您可能根本不知道此功能可用，而不是有真正的原因您想要自己实现并以相当奇怪的方式进行方式。

如果我错了，并且上面的指针对你没有用，我建议你将你的实现调整为标准版本的接口（尽可能多）并解释你为什么不想使用STL 版本，因为这些步骤将增加 StackOverflow 用户（可能比我回答您的问题的人，以及未来有类似问题的用户）对您的代码的熟悉度。