Java Comparator Hackerrank Solution with Explanation | Programming Blog

Comparing Objects with Comparator in Java | Compare and Sort two Objects in Java

Comparators are used to compare two objects. In this challenge, you'll create a comparator and use it to sort an array.

The Player class is provided for you in your editor. It has 2 fields : a name string and score integer.

Given an array of n Player objects, write a comparator that sorts them in order of decreasing score; if 2 or more players have the same score, sort those players alphabetically by name. To do this, you must create a Checker class that implements the Comparator interface, then write an int compare(Player a, Player b) method implementing the Comparator.compare(T o1, T o2) method.

Input Format

Input from stdin is handled by the locked stub code in the Solution class.
The first line contains an integer, n, denoting the number of players.
Each of the n subsequent lines contains a player's name and score, respectively.

Read full description on Hackerrank Website :-

• https://www.hackerrank.com/challenges/java-comparator/problem 

So let's see solution of above problem.

If you want to learn about Comparator interface in java. Check out below link :-

• Comparator interface with Examples

Solution 1 :-

import java.util.*;

// Write your Checker class here

class Checker implements Comparator<Player> {
    @Override
    public int compare(Player o1, Player o2) {
       if (o1.score > o2.score) {
           return -1;
       } if (o1.score < o2.score) {
           return 1;
       } if (o1.score == o2.score) {
           return o1.name.compareTo(o2.name);
       }
    return 0;
    } 
}


class Player{
    String name;
    int score;
    
    Player(String name, int score){
        this.name = name;
        this.score = score;
    }
}

class Solution {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();

        Player[] player = new Player[n];
        Checker checker = new Checker();
        
        for(int i = 0; i < n; i++){
            player[i] = new Player(scan.next(), scan.nextInt());
        }
        scan.close();
     
        Arrays.sort(player, checker);
        for(int i = 0; i < player.length; i++){
            System.out.printf("%s %s\n", player[i].name, player[i].score);
        }
    }
}

Input and Output :-

Input
5
amy 100
david 100
heraldo 50
aakansha 75
aleksa 150

Output
aleksa 150
amy 100
david 100
aakansha 75
heraldo 50 

Explanation :-

• Created one Checker class as given instruction. And implements Comparator in Checker class.
• If you implements Comparable interface then you must to Override its compare method. Same we done in above example.
• compare functions returns negative integer, zero, or a positive integer, -1, 0, 1.(In Increment order, In decrement order below things are done in Reverse)
• Return Negative integer (-1) :- When First argument is Less than Second argument.
  
• Return Positive integer (1) :- When First argument is Greater than Second argument.
• Return 0 :- When First argument is Equals to Second argument. 
•  So, first we check score and if score are same for two objects then we check compare using name, and returns based on that.

We can also minimize above solution.

Solution 2 :-

class Checker implements Comparator<Player> {
    @Override
    public int compare(Player p1, Player p2) {
        if (p1.score == p2.score) {
            return p1.name.compareTo(p2.name);
        } else {
            return p2.score - p1.score;
        }
    }
} 

Solution 3 :-

class Checker implements Comparator<Player> {
    @Override
    public int compare(Player o1, Player o2) {
     return (o2.score == o1.score) 
        ? o1.name.compareTo(o2.name) 
        : o2.score - o1.score;
    }
}

Explanation :-

Here we doing same thing as above solution. 

• If both objects mark property are same then compare using name property, otherwise compare using score.

 

Happy Coding..

 

Comparing Objects with Comparable interface in Java :-

• Comparable Interface in Java with Examples | How Comparable Interface works in Java? 

Sort Object with NULL values using Comparator interface in Java

• Sort java List by Object property with null check using Comparator | Java 8 Lambda