Topic

Comparable

Problem

Leaderboard

There is an application to create leaderboards of e-sports competitions. It uses the Score class to represent a score of each player. This class has two fields: player for the player's name and totalScore for that player's total score. To build a leaderboard, the Score objects need to be compared. A Score object is considered bigger than another Score if it's totalScore value is bigger. If totalScore values of two Score objects are the same, such objects must be compared by their player values. See the example below.

Code of problem

import java.util.*;

class Score implements Comparable<Score> {
    private final String player;
    private final int totalScore;

    public Score(String player, int totalScore) {
        this.player = player;
        this.totalScore = totalScore;
    }

    public String getPlayer() {
        return player;
    }

    public int getTotalScore() {
        return totalScore;
    }

    @Override
    public String toString() {
        return player + '=' + totalScore;
    }

    @Override
    public int compareTo(Score score) {
        // your code here
    }
}

// do not change the code below
class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        List<Score> scores = new ArrayList<>();
        while (sc.hasNextLine()) {
            String[] input = sc.nextLine().split(" ");
            Score score = new Score(input[0], Integer.parseInt(input[1]));
            scores.add(score);
        }

        Collections.sort(scores);
        System.out.println(scores);
    }
}

Hint & Explain

compare both fields (score then player)

Solution

My solution

// your code here
if (getTotalScore() > score.getTotalScore()) return 1;
else if (getTotalScore() < score.getTotalScore()) return -1;
else {
    return getPlayer().compareTo(score.getPlayer());
}

BAD!

Other solution 1

// your code here
int result = Integer.compare(totalScore, score.totalScore);
return result == 0 ? player.compareTo(score.player) : result;

Other solution 2

// your code here
if (totalScore == score.totalScore) {
    return player.compareTo(score.player);
} else {
    return Integer.compare(totalScore, score.totalScore);
}