[英]priority queue sort [C++]
我要交一個作業,這要求我向我上次作業所做的優先級隊列添加排序方法。
好吧,我確實添加了sort函數,但是我不確定如何用它完成我的main,因為main似乎已經對隊列進行了排序。 我確實有一個主要的樣子的例子,但我相信教授希望我們處理之前提交的內容,因此我堅持要做的事情。 請幫忙。
哦,我的上次作業沒有加分,他只剩下一個要發表評論的內容:“在調用enqueue()時出現段錯誤。” 我給他發送了一封電子郵件,這意味着什么,他沒有回復(昨天取消了成績)。 我認為錯誤是由於第90行未調用malloc
。
#include <stdlib.h> //NEEDED TO RUN calloc
#include <cstdio> // NEEDED TO RUN perror
#include <iostream>
using namespace std;
// c-style struct
// node used to implement linked list
typedef struct _node
{
int value;
struct _node *next;
}
node;
/* Standard Stack LIFO ADT */
class Priority_Queue
{
/* tracks number of nodes in Priority_Queue */
int nNodes;
/* keeps track of first node in Priority_Queue */
node *head;
void sort( void ); //Sort linked list using selection sorting algorithm
//anything above public is private
public:
Priority_Queue( void ); //find a constructor everytime the user extanjiates Priority_Queue object.
void enqueue( int ); //insert node/ enqueue on an integer.
void dequeue( void ); //remove node/ dequeue off node from the top.
bool empty( void ); //test whether Priority_Queue is empty
int size( void ); //return size
int top( void ); // access top of the Priority_Queue/ next node.
int back( void );
};
/* init head and nNodes */
Priority_Queue::Priority_Queue( void )
{
head = NULL; //everytime a user enstantiates one of the Priority_Queues
nNodes = 0; // so we know how many nodes are sitting on our Priority_Queue.
}
/* place new node at top of Priority_Queue */
void Priority_Queue::enqueue( int value ) //enqueue on a value/ user wants to place a Priority_Queue
{
if( head == NULL )
{
if(( head = (node*)calloc(1, sizeof(node))) == NULL )
{
perror( "Could not calloc memory" );
}
else
{
head->value = value;
nNodes++; // increase the number of nodes in link list
}
}
else
{
node *temp;
if( ( temp = (node*)malloc( sizeof( node ) ) ) == NULL ) //malloc because both values for stut will be set immediatly
{
perror( "Could not malloc memory" );
}
else
{
temp->value = value; //
node* p = head;
if ( value<head->value )
{
temp -> next = head;
head = temp;
temp = NULL;
}
while (p->next != NULL && p->next->value<value )
{
p = p-> next; // p is pointintint to the next node
}
temp->next = p->next;
p->next = temp;
temp = NULL;
nNodes++; // increase the number of nodes in link list
}
//malloc( sizeof (node));
}
}
/* remove the first node from top of Priority_Queue */
void Priority_Queue::dequeue( void )
{
node *temp;
if( head != NULL ) // allow users to keep calling dequeue even if it is empty
{
temp = head;
head = head->next; // head is now pointing to 3
free( temp );
temp = NULL;
nNodes--; //decrease node count for the Priority_Queue
}
}
/* return true if Priority_Queue is empty */
bool Priority_Queue::empty( void )
{
return ( head == NULL ); //valuated as true or false.
}
/* return number of nodes in Priority_Queue */
int Priority_Queue::size( void )
{
return nNodes; //PLACING RESPONSIBILITY ON USER TO REMEMBER 28:00 part1
}
/* return value of node at top of Priority_Queue */
int Priority_Queue::top( void )
{
return head->value; // PLACING RESPONSIBILITY ON USER TO REMEMBER 28:00 part1
}
int Priority_Queue::back( void )
{
node *p = head;
while (p->next != NULL)
{
p = p->next;
}
return p->value; //
}
void Priority_Queue::sort( void )
{
node *temp;
bool onward = true; //while loop set to true
//compare each pair of adjacent elements
//switches elements if in wrong order
//Continues operations until elements are sorted.
while( onward )
{
// onward set to false so just in case it is sorted, it will loop through the elements.
for( temp = head, onward = false; temp->next != NULL; temp = temp->next )
{
//Check to see if current element is greater than the next
if( temp->value > temp->next->value )
{
//swapping current elements value
int a = temp->value;
temp->value = temp->next->value;
temp->next->value = a;
onward = true; //
}
}
}
}
int main( void )
{
/* instantiate new Priority_Queue */
Priority_Queue my_Priority_Queue = Priority_Queue();
int i = 0;
/* enqueue some values onto Priority_Queue */
for( i = 0; i < 10; i++ )
my_Priority_Queue.enqueue( i );
/* print values stored in Priority_Queue until Priority_Queue is empty */
while( !my_Priority_Queue.empty() )
{
cout << "Value: " << my_Priority_Queue.top() << endl; // Give access to the top of the Priority_Queue.
my_Priority_Queue.dequeue(); // dequeue the top off so to see a different node at the top in the next line.
cout << "Node Count: " << my_Priority_Queue.size() << endl << endl;
}
my_Priority_Queue.dequeue();
return 0;
}
優先級隊列通常具有獲取最高優先級元素的功能。
要對所有元素進行排序,您需要做的就是將元素一個接一個地彈出,它們將按照排序的順序排列。
通常,將優先級隊列實現為堆,將使用堆作為優先級隊列的排序算法稱為堆排序。
由於沒有給您優先級隊列代碼,因此以std :: priority_queue為例,以下是獲取元素排序列表的方法:
template<class T, class Container, class Compare>
std::vector<T> get_sorted(std::priority_queue<T, Container, Compare> pq)
{
std::vector<T> sorted;
sorted.reserve(pq.size());
while (!pq.empty())
{
sorted.push_back(pq.top());
pq.pop();
}
return sorted;
}
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