Sorting: Comparator - Hacker Rank Solution

Check out the resources on the page's right side to learn more about sorting. The video tutorial is by Gayle Laakmann McDowell, author of the best-selling interview book Cracking the Coding Interview.

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 in the editor below. It has two fields:

1. : a string.
2. : an integer.

Given an array of  Player objects, write a comparator that sorts them in order of decreasing score. If  or more players have the same score, sort those players alphabetically ascending 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. In short, when sorting in ascending order, a comparator function returns  if ,  if , and  if .

For example, given  Player objects with  values of , we want to sort the list as .

Function Description

Declare a Checker class that implements the comparator method as described. It should sort first descending by score, then ascending by name. The code stub reads the input, creates a list of Player objects, uses your method to sort the data, and prints it out properly.

Input Format

Locked stub code in the Solution class handles the following input from stdin:

The first line contains an integer, , the number of players. 
Each of the next  lines contains a player's respective  and , a string and an integer.

Constraints

• Two or more players can have the same name.
• Player names consist of lowercase English alphabetic letters.

Output Format

You are not responsible for printing any output to stdout. Locked stub code in Solution will create a Checker object, use it to sort the Player array, and print each sorted element.

Sample Input

5
amy 100
david 100
heraldo 50
aakansha 75
aleksa 150

Sample Output

aleksa 150
amy 100
david 100
aakansha 75
heraldo 50

Explanation

As you can see, the players are first sorted by decreasing score and then sorted alphabetically by name.

Sorting: Comparator - Hacker Rank Solution

You have to check at least a.score versus b.score, and in the case of a tie, a.name versus b.name. For an ascending sort, return -1, 0, 1 for a < b, a = b and a > b. For descending, return 1, 0, -1 for a < b, a = b and a > b. An implementation is shown below.

Problem Tester's code:

import java.util.*;

class Checker implements Comparator<Player>{

    public int compare(Player a, Player b) {
        // If 2 Players have the same score
        if(a.score == b.score){
            // Order alphabetically by name
            if(a.name.compareTo(b.name) < 0){
                return -1;
            }
            else if(a.name.compareTo(b.name) > 0){
                return 1;
            }
            return 0;
        }    
        
        // Otherwise, order higher score first   
        else if(a.score > b.score){
            return -1;
        }
        else if(a.score < b.score){
            return 1;
        }
        
        return 0;
    }
}

/** Alternative Approach:

    class Checker implements Comparator<Player>{

        public int compare(Player a, Player b) {
            // If 2 Players have the same score
            if(a.score == b.score){
                // Order alphabetically by name
                return a.name.compareTo(b.name);
            }    

            // Otherwise, order higher score first  
            return ((Integer) b.score).compareTo(a.score);
        }
    }

**/

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);
        }
    }
}