The use of Priority_queue

Priority_queue calls STL's Make_heap (), Pop_heap (), PUSH_HEAP () algorithm implementations, which is another form of heap. Write a priority_queue that is similar to the Priority_queue usage in the real STL using the STL heap algorithm to deepen the understanding of priority_queue.

#include <iostream> #include <algorithm> #include <vector>using namespace Std;class priority_queue{    Private:        vector<int> data;            Public:        void push (int t) {             data.push_back (t);             Push_heap (Data.begin (), Data.end ());         }                void Pop () {            pop_heap (Data.begin (), Data.end ());            Data.pop_back ();        }                int Top () {return Data.front ();}        int size () {return data.size ();}        bool Empty () {return data.empty ();}}; int main () {    priority_queue test;    Test.push (3);    Test.push (5);    Test.push (2);    Test.push (4);        while (!test.empty ()) {        cout << test.top () << Endl;        Test.pop (); }            return 0;}

 The priority_queue in STL is similar in that it only adds templates and related iterators.

Priority_queue is relatively simple to use for basic types. His template declaration has three parameters: priority_queue<type, Container, functional> where type is the data type, Container is the container that holds the data, functional The method for comparing elements. Container must be an array-implemented container, such as a vector, deque but not a list.
In the STL, the vector is used by default. The comparison is by default with operator<, so if you put the next two parameters by default, the priority queue is the Big Top heap, the team head element is the largest.  

#include <iostream> #include <queue>using namespace Std;int main () {    priority_queue<int> q;        for (int i= 0; i<; ++i) Q.push (rand ());    while (!q.empty ()) {        cout << q.top () << Endl;        Q.pop ();    }        GetChar ();    return 0;}

If you want to use a small top heap, you generally have to take the template three parameters are taken in. The STL defines a functor Greater<&gt, and for a basic type you can declare a small top heap with this functor

#include <iostream> #include <queue>using namespace Std;int main () {    priority_queue<int, vector< Int>, greater<int> > Q;        for (int i= 0; i<; ++i) Q.push (rand ());    while (!q.empty ()) {        cout << q.top () << Endl;        Q.pop ();    }        GetChar ();    return 0;}

For custom types, you must overload the operator< yourself or write your own copy function

#include <iostream> #include <queue>using namespace std;struct node{    int x, y;    Node (int a= 0, int b= 0):        x (a), Y (b) {}};bool operator< (Node A, Node B) {    if (a.x== b.x) return a.y> b.y ;    return a.x> b.x; }int Main () {    priority_queue<node> q;        for (int i= 0; i<; ++i)    Q.push (Node (rand (), Rand ()));        while (!q.empty ()) {        cout << q.top (). x << ' << q.top (). y << Endl;        Q.pop ();    }        GetChar ();    return 0;}

After the custom type overloads the operator<, the object can be declared with only one template parameter.
But it can't be declared like a basic type at this point
Priority_queue<node, Vector<node>, greater<node> >;
The reason is that greater<node> is not defined, and if you want to define it this way, you can do so as follows:  

#include <iostream> #include <queue>using namespace std;struct node{    int x, y;    Node (int a= 0, int b= 0):        x (a), Y (b) {}};struct cmp{    bool Operator () (Node A, Node B) {        if (a.x== b.x) ret Urn a.y> b.y;                return a.x> b.x; }};int Main () {    priority_queue<node, vector<node>, cmp> Q;        for (int i= 0; i<; ++i)    Q.push (Node (rand (), Rand ()));        while (!q.empty ()) {        cout << q.top (). x << ' << q.top (). y << Endl;        Q.pop ();    }        GetChar ();    return 0;} The above code implements a small top heap

The use of Priority_queue