将多个项目添加到具有固定大小数组的优先级队列时出错

Posted 2023-02-16

【中文标题】将多个项目添加到具有固定大小数组的优先级队列时出错

【英文标题】：Error Adding Multiple Items to a Priority Queue with a Fixed Size Array

【发布时间】：2017-04-19 23:36:32

【问题描述】：

在我们开始之前，是的，这是家庭作业。

希望我能在这里得到一些澄清。我正在实现一个具有固定大小数组的优先级队列，并且编写了所有函数并且一切都编译了，但是我在测试文件中的选项 M 有问题。所有其他函数都可以正常工作，但是当我尝试add_multiple_items 时，swap_with_parent 函数的断言中出现表达式错误。这是我的程序文件。 pqtest2.cpp 文件：

// FILE: pqtest2.cpp
// An interactive test program for the Priority Queue class
#include <cctype>     // Provides toupper
#include <iostream>  // Provides cout and cin
#include <cstdlib>    // Provides EXIT_SUCCESS and size_t
#include "pqueue2.h"   // Implemented using a heap
using namespace std;

// PROTOTYPES for functions used by this test program:
void print_menu( );
char get_user_command( );
int get_number(const char message[ ]);
void add_multiple_entries(PriorityQueue &q);

int main( )

    PriorityQueue test;
    char choice;
    cout << "CSC-161 Lesson Ten Test Program" << endl << endl;
    do

    print_menu( );
    choice = toupper(get_user_command( ));
    switch (choice)
    
        case 'E':
            if (test.is_empty( ))
                cout << "The Priority Queue is empty." << endl;
            else
                cout << "The Priority Queue is not empty." << endl;
            break;
        case 'G':
            if (!test.is_empty( ))
                cout << "Front item is: " << test.get_front( ) << endl;
            else
                cout << "There is no current item." << endl;
            break;
        case 'I':
            test.insert(get_number("Please enter the next item: "),
                (unsigned int) get_number("The item's priority: "));
            break;
        case 'M':
            add_multiple_entries(test);
            break;
        case 'P':
            test.print_tree("Contents of heap:");
            break;
        case 'S': 
            cout << "The size is " << test.size( ) << endl;
            break;
        case 'X': 
            if (test.is_empty( ))
                cout << "The Priority Queue is empty." << endl;
            else
                while(!test.is_empty())
                    cout << "Value: " << test.get_front() << endl;
            break;
        case 'Q': 
            break;
        default:  
            cout << choice << " is an invalid choice." << endl;
    

while ((choice != 'Q'));
return EXIT_SUCCESS;


void print_menu( )

    cout << endl; 
cout << "The following choices are available: " << endl;
cout << " E   Print the result from the is_empty( ) function" << endl;
cout << " G   Print the result from the get_front( ) function" << endl;
cout << " I   Insert a new item with the insert(...) function" << endl;
cout << " M   Add multiple items with varying priorities " << endl;
cout << " P   Print the internal heap using the print_tree(...) function" << endl;
cout << " S   Print the result from the size( ) function" << endl;
cout << " X   Extract and print values in priority order" << endl;
cout << " Q   Quit this test program" << endl;


char get_user_command( )

char command;
cout << "\nEnter choice: ";
cin >> command; 
return command;


int get_number(const char message[ ])

int result;
cout << message;
cin  >> result;
return result;

void add_multiple_entries(PriorityQueue &thisQueue)

thisQueue.insert(100, 10);
thisQueue.insert(200, 10);
thisQueue.insert(300, 5);
thisQueue.insert(400, 5);
thisQueue.insert(500, 20);
thisQueue.insert(600, 20);
thisQueue.insert(700, 20);
thisQueue.insert(800, 10);
thisQueue.insert(900, 10);
return;

pqueue.h 文件：

// FILE: pqueue2.h
// CLASS PROVIDED: PriorityQueue (a priority queue of items)
//
// TYPEDEF and MEMBER CONSTANT for the PriorityQueue class:
//   static const size_t CAPACITY = ______
//     PriorityQueue::CAPACITY is the maximum number of entries that
//     may be be in the priority queue at any one time.
//
//   typedef _____ Item 
//     The type Item is the data type of the items in the Priority Queue.
//     It may be any of the C++ built-in types (int, char, etc.), or a class 
//     with a default constructor, a copy constructor, and assignment operator.
//
// CONSTRUCTOR for the PriorityQueue class:
//   PriorityQueue( )
//     Postcondition: The PriorityQueue has been initialized with no Items.
//
// MODIFICATION MEMBER FUNCTIONS for the PriorityQueue class:
//   void insert(const Item& entry, unsigned int priority)
//     Postcondition: A new copy of entry has been inserted with the specified
//     priority.
//
//   Item get_front( )
//     Precondition: size( ) > 0.
//     Postcondition: The highest priority item has been returned and has been
//     removed from the PriorityQueue. (If several items have equal priority,
//     then there is no guarantee about which one will come out first!
//     This differs from our first priority queue.)
//
// CONSTANT MEMBER FUNCTIONS for the PriorityQueue class:
//   size_t size( ) const
//     Postcondition: Return value is the total number of items in the
//     PriorityQueue.
//
//   bool is_empty( ) const
//     Postcondition: Return value is true if the PriorityQueue is empty.
//
// VALUE SEMANTICS for the PriorityQueue class:
//   Assignments and the copy constructor may be used with
//   PriorityQueue objects

#ifndef PQUEUE_H
#define PQUEUE_H
#include <cstdlib> // Provides size_t

    class PriorityQueue
    
    public:
        // TYPEDEF and MEMBER CONSTANT
        typedef double Item;
        static const size_t CAPACITY = 5000;
        // CONSTRUCTOR
        PriorityQueue( );
        // MODIFICATION MEMBER FUNCTIONS
        void insert(const Item& entry, unsigned int priority);
        Item get_front( );
        // CONSTANT MEMBER FUNCTIONS
        size_t size( ) const  return many_items; 
        bool is_empty( ) const  return (many_items == 0); 
        // MEMBER FUNCTION FOR DEBUGGING
        void print_tree(const char message[ ] = "", size_t i = 0) const;
    private:
        // STRUCT DEFINITION to store information about one item in the pqueue
        struct OneItemInfo
        
            Item data;
            unsigned int priority;
        ;
        // PRIVATE MEMBER VARIABLES
        OneItemInfo heap[CAPACITY];
        size_t many_items;
        // PRIVATE HELPER FUNCTIONS -- see pqueue2.cxx for documentation
        bool is_leaf(size_t i) const;
        size_t parent_index(size_t i) const;
        unsigned int parent_priority(size_t i) const;
        size_t big_child_index(size_t i) const;
        unsigned int big_child_priority(size_t i) const;
        void swap_with_parent(size_t i);
    ;

#endif

pqueue2.cpp 文件：

// FILE: pqueue2.cpp
// IMPLEMENTS: PriorityQueue (See pqueue2.h for documentation.)
// IMPLEMENTED BY: Michael Main ([e-mail])
// 
//  Alex Chapman ID: S02084651
//
//
// INVARIANT for the PriorityQueue Class:
//   1. The member variable many_items is the number of items in the
//      PriorityQueue.
//   2. The items themselves are stored in the member variable heap,
//      which is a partially filled array organized to follow the usual
//      heap storage rules from Chapter 11 of the class notes.
// NOTE: Private helper functions are implemented at the bottom of this
// file along with their precondition/postcondition contracts.

#include <cassert>    // Provides assert function
#include <iostream>  // Provides cin, cout
#include <iomanip>   // Provides setw
#include <cmath>      // Provides log2
#include "pqueue2.h"
using namespace std;

PriorityQueue::PriorityQueue( )

    heap[CAPACITY];
    many_items = 0;


void PriorityQueue::insert(const Item& entry, unsigned int priority)

    if (many_items == 0)
    
        heap[many_items].data = entry;
        heap[many_items].priority = priority;
        many_items++;
    
    else
    
        heap[many_items].data = entry;
        heap[many_items].priority = priority;
        unsigned int i = many_items;
        many_items++;

        while(parent_priority(i) < priority)
        
            swap_with_parent(i);
            i = parent_index(i);
        
    


PriorityQueue::Item PriorityQueue::get_front( )

    assert(many_items > 0);
    if (many_items == 1)
    
        Item front_value = heap[0].data;
        many_items--;
        return front_value;
    
    else
    
        Item front_value = heap[0].data;
        heap[0] = heap[many_items - 1];
        unsigned int priority = heap[many_items - 1].priority;
        unsigned int k = 0;

        while((k < many_items) && !is_leaf(k) && big_child_priority(k) > priority)
        
            unsigned int j = big_child_index(k);
            swap_with_parent(big_child_index(k));
            k = j;
        
        many_items--;
        return front_value;
    


bool PriorityQueue::is_leaf(size_t i) const
// Precondition: (i < many_items)
// Postcondition: If heap[i] has no children in the heap, then the function
// returns true. Otherwise the function returns false.

    if (2 * i + 1 >= many_items)
    
        return 1;
    
    else
    
        return 0;
    


size_t PriorityQueue::parent_index(size_t i) const
// Precondition: (i > 0) && (i < many_items)
// Postcondition: The return value is the index of the parent of heap[i].

    return (i - 1) / 2;


unsigned int PriorityQueue::parent_priority(size_t i) const
// Precondition: (i > 0) && (i < many_items)
// Postcondition: The return value is the priority of the parent of heap[i].

    return heap[(i - 1) / 2].priority;


size_t PriorityQueue::big_child_index(size_t i) const
// Precondition: !is_leaf(i)
// Postcondition: The return value is the index of one of heap[i]'s children.
// This is the child with the larger priority.

    assert(!is_leaf(i));

    if ((2 * i) + 2 < many_items)
    
        if (heap[(2 * i) + 1].priority > heap[(2 * i) + 2].priority)
        
            return (2 * i) + 1;
        
        else
        
            return (2 * i) + 2;
        
    
    else
    
        return (2 * i) + 1;
    


unsigned int PriorityQueue::big_child_priority(size_t i) const
// Precondition: !is_leaf(i)
// Postcondition: The return value heap[big_child_index(i)].priority

    return heap[big_child_index(i)].priority;


void PriorityQueue::swap_with_parent(size_t i)
// Precondition: (i > 0) && (i < many_items)
// Postcondition: heap[i] has been swapped with heap[parent_index(i)]

    assert (i>0 && i< many_items);
    OneItemInfo temp_parent = heap[parent_index(i)];
    OneItemInfo temp_child = heap[i];
    heap[i] = temp_parent;
    heap[parent_index(i)] = temp_child;


void PriorityQueue::print_tree(const char message[ ], size_t i) const
// Postcondition: If the message is non-empty, then that has been written
// to cout. After the message, the portion of the heap with root at node
// node i has been written to the screen. Each node's data is indented
// 4*d, where d is the depth of the node.
// NOTE: The default argument for message is the empty string, and the
// default argument for i is zero. For example, to print the entire
// tree of a PriorityQueue p, with a message of "The tree:", you can call:
//     p.print_tree("The tree:");
// This call uses i=0, which prints the whole tree.

    const char NO_MESSAGE[] = "";
    size_t depth;

    if (message[0] != '\0')
    
        cout << message << endl;
    
    if (i > many_items)
    
        cout << "No Nodes" << endl;
    
    else
    
        depth = int(log(double(i + 1))/log(2.0));
        cout << setw(depth * 4) << "";
        cout << heap[i].data;
        cout << " (priority " << heap[i].priority << ")" << endl;

        if (2 * i + 1 < many_items)
        
            print_tree(NO_MESSAGE, 2 * i + 1);
        
        if (2 * i + 2 < many_items)
        
            print_tree(NO_MESSAGE, 2 * i + 2);
        
    

我还附上了错误图片。

【问题讨论】：

此断言在哪个插入上失败？将一些 printfs 放在那里或在调​​试器中跟随。

【参考方案1】：

while(parent_priority(i) < priority)

即使i == 0，你也一直在寻找父母。改成while (i > 0 && parent_priority(i) < priority)。