STL Priority Queue for Structure or Class
STL priority_queue is the implementation of Heap Data-structure. By default, it’s a max heap and we can easily use it for primitive datatypes. There are some important applications of it which can be found here
Prerequisite: Prioirty_queue Basics
In this article, we will see how can we use priority_queue for custom datatypes like class or structure.
suppose we have a structure name Person which consist of two variables Age and height
and we want to store that that in priority_queue then a simple method won’t work here.
Given below is an example of the declaration of struct Person:
C++
struct Person{int Age;float Height;} |
On defining the Priority Queue as shown below, it’ll give us error since priority_queue doesn’t know on what order(min or max) we need to arrange the objects.
C++
priority_queue<Person> pq; |
To rectify the error above, we will use operator overloading to define the priority. So that priority_queue can decide how to store the structure object.
Given below is the priority_queue implementation with the structure below:
C++
// program in c++ to use priority_queue with structure#include <iostream>#include <queue>using namespace std;#define ROW 5#define COL 2struct Person { int age; float height; // this will used to initialize the variables // of the structure Person(int age, float height) : age(age), height(height) { }};// this is an structure which implements the// operator overloadingstruct CompareHeight { bool operator()(Person const& p1, Person const& p2) { // return "true" if "p1" is ordered // before "p2", for example: return p1.height < p2.height; }};int main(){ priority_queue<Person, vector<Person>, CompareHeight> Q; // When we use priority_queue with structure // then we need this kind of syntax where // CompareHeight is the functor or comparison function float arr[ROW][COL] = { { 30, 5.5 }, { 25, 5 }, { 20, 6 }, { 33, 6.1 }, { 23, 5.6 } }; for (int i = 0; i < ROW; ++i) { Q.push(Person(arr[i][0], arr[i][1])); // insert an object in priority_queue by using // the Person structure constructor } while (!Q.empty()) { Person p = Q.top(); Q.pop(); cout << p.age << " " << p.height << "\n"; } return 0;} |
Output :
33 6.1 20 6 23 5.6 30 5.5 25 5
Given below is the implementation of priority_queue using Class
C++
// program in c++ to use priority_queue with class#include <iostream>#include <queue>using namespace std;#define ROW 5#define COL 2class Person {public: int age; float height; // this is used to initialize the variables of the class Person(int age, float height) : age(age), height(height) { }};// we are doing operator overloading through thisbool operator<(const Person& p1, const Person& p2){ // this will return true when second person // has greater height. Suppose we have p1.height=5 // and p2.height=5.5 then the object which // have max height will be at the top(or // max priority) return p1.height < p2.height;}int main(){ priority_queue<Person> Q; float arr[ROW][COL] = { { 30, 5.5 }, { 25, 5 }, { 20, 6 }, { 33, 6.1 }, { 23, 5.6 } }; for (int i = 0; i < ROW; ++i) { Q.push(Person(arr[i][0], arr[i][1])); // insert an object in priority_queue by using // the Person class constructor } while (!Q.empty()) { Person p = Q.top(); Q.pop(); cout << p.age << " " << p.height << "\n"; } return 0;} |
Output :
33 6.1 20 6 23 5.6 30 5.5 25 5
