Priority Queue Basic Usage

Http://www.cnblogs.com/void/archive/2012/02/01/2335224.html

Priority Queue Priority_queue Usage

A priority queue is one of the queues, but it can dynamically sort the data in a queue in a way that is customized (priority of the data)

Each push and pop operation, the queue is dynamically adjusted to the way we expect it to be stored.

For example: Our common operation is to sort the data, Priority Queue default is the high priority of the data

So, regardless of the order in which we push a bunch of numbers, we end up in the queue always top out the largest element.

Usage:

Example: Push the element 5,3,2,4,6 to the priority queue and print its output.

1. The standard library uses the < operator of the element type by default to determine the precedence relationship between them.

priority_queue<int> PQ;

The < operator shows the high precedence of the elements in integers.
Therefore, the output in Example 1 is: 6 5 4 3 2

2. The smaller the data, the higher the priority

priority_queue<int, vector<int>, greater<   

which
The second parameter is a container type.
The second argument is a comparison function.
Therefore, the output in Example 2 is: 2 3 4 5 6

3. Custom priority, overloaded comparison symbol

Overloading Default < Symbols

struct node
{
    operator< (node n1, node N2)
    {
        return n1.priority < n2.priority;
    }
    int priority;
    int value;

At this point, you need to customize a priority for each element.

Note: The overload > number compiles an error because the standard library uses the < operator of the element type by default to determine the precedence relationship between them.
and the < operator of the custom type has no direct contact with the > operator

Code:

1 #include <iostream>
2 #include <functional>
3 #include <queue>
4Using Namespace stdnamespace std;
5struct node
6 {
7 Friendbooloperator< (node n1, node N2)
: 9
9return n1.priority < n2.priority;
10}
11int priority;
12int value;
13};
14int main ()
15 {
16Constint len =5;
17int i;
18int A[len] = {3,5,9,6,2};
19//Example 1
priority_queue<Int> Qi;
21stfor (i =0; i < Len; i++)
Qi.push (A[i]);
23for (i =0; i < Len; i++)
24 {
Cout<<qi.top () <<"";
Qi.pop ();
27}
cout<<endl;
29//Example 2
priority_queue<int, vector<Int>, greater<Int> >qi2;
31for (i =0; i < Len; i++)
Qi2.push (A[i]);
33for (i =0; i < Len; i++)
34 {
Cout<<qi2.top () <<"";
Qi2.pop ();
37}
cout<<endl;
39//Example 3
Priority_queue<node> qn;
+ node B[len];
b[0].priority =6; b[0].value =1;
b[1].priority =9; b[1].value =5;
b[2].priority =2; b[2].value =3;
b[3].priority =8; b[3].value =2;
b[4].priority =1; b[4].value =4;
47
48for (i =0; i < Len; i++)
Qn.push (B[i]);
cout<<"Priority level "<< \t ' << '  value  ' < <endl; 
 51 for (i = 0; I < Len i++) 
 52 {
 53 cout<<qn.top () .priority< < ' \t << Qn.top () .value<<endl; 
 54 Qn.pop (); 
 55} 
 56 return 0; 
 57}             

Priority Queue Basic usage