[Hacker Rank] Interview Preparation Kit: Sorting: Comparator. Solved ✅.

Author: Gonzalo Diaz

docs/hackerrank/interview_preparation_kit/sort/ctci-comparator-sorting.md

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+# [Sorting: Comparator](https://www.hackerrank.com/challenges/ctci-comparator-sorting)
+
+Write a Comparator for sorting elements in an array.
+
+- Difficulty:  `#medium`
+- Category: `#ProblemSolvingBasic` `#sorting`
+
+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. `name`: a string.
+2. `score`: an 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 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)](https://docs.oracle.com/javase/7/docs/api/java/util/Comparator.html#compare(T,%20T))
+method.
+In short, when sorting in ascending order,
+a comparator function returns `-1` if `a < b`,
+`0` if `a = b`, and `1` if `a > b`.
+
+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.
+
+## Example
+
+`n = 3`
+`data = [[Smith, 20], [Jones, 15], [Jones, 20]]`
+
+Sort the list as $ data_{sorted} $ = `[Jones, 20], [[Smith, 20], [Jones, 15]]`.
+Sort first descending by score, then ascending by name.
+
+## Input Format
+
+The first line contains an integer, `n`, the number of players.
+Each of the next `n` lines contains a player's `name` and `score`,
+a string and an integer.
+
+## Constraints
+
+- $ 0 \leq score \leq 1000 $
+- 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 instantiate a Checker object,
+use it to sort the Player array, and print each sorted element.
+
+## Sample Input
+
+```text
+5
+amy 100
+david 100
+heraldo 50
+aakansha 75
+aleksa 150
+```
+
+## Sample Output
+
+```text
+aleksa 150
+amy 100
+david 100
+aakansha 75
+heraldo 50
+```
+
+## Explanation
+
+The players are first sorted descending by score, then ascending by name.

src/hackerrank/interview_preparation_kit/sort/ctci_comparator_sorting.test.ts

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+import { describe, expect, it } from '@jest/globals';
+
+import {
+  Player,
+  SortablePlayer,
+  comparatorSorting,
+  comparatorSortingPrint
+} from './ctci_comparator_sorting';
+import TEST_CASES from './ctci_comparator_sorting.testcases.json';
+
+describe('countSwaps', () => {
+  it('test_player', () => {
+    expect.assertions(2);
+
+    const aPlayer = new Player('David', 100);
+    const aPlayerAsString = aPlayer.toString();
+    const aExpected = '';
+
+    expect(aExpected).toStrictEqual(aPlayerAsString);
+
+    const bPlayer = new Player('Kurt', 10);
+    const comparatorAnswerExpected = 0;
+
+    expect(aPlayer.comparator(bPlayer)).toStrictEqual(comparatorAnswerExpected);
+  });
+
+  it('test_comparator_sorting', () => {
+    expect.assertions(8);
+
+    TEST_CASES.forEach((test) => {
+      const players: SortablePlayer[] = [];
+
+      for (const player of test.input) {
+        players.push(new SortablePlayer(player.name, player.score));
+      }
+
+      expect(comparatorSorting(players)).toStrictEqual(test.sorted);
+      expect(comparatorSortingPrint(players)).toBeUndefined();
+    });
+  });
+});

src/hackerrank/interview_preparation_kit/sort/ctci_comparator_sorting.testcases.json

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+[
+  {
+    "title": "Sample Test Case 0",
+    "input": [
+      {
+        "name": "amy",
+        "score": 100
+      },
+      {
+        "name": "david",
+        "score": 100
+      },
+      {
+        "name": "heraldo",
+        "score": 50
+      },
+      {
+        "name": "aakansha",
+        "score": 75
+      },
+      {
+        "name": "aleksa",
+        "score": 150
+      }
+    ],
+    "sorted": ["aleksa 150", "amy 100", "david 100", "aakansha 75", "heraldo 50"],
+    "expected": "aleksa 150\namy 100\ndavid 100\naakansha 75\nheraldo 50"
+  },
+  {
+    "title": "Sample Test Case 6",
+    "input": [
+      {
+        "name": "smith",
+        "score": 20
+      },
+      {
+        "name": "jones",
+        "score": 15
+      },
+      {
+        "name": "jones",
+        "score": 20
+      }
+    ],
+    "sorted": ["jones 20", "smith 20", "jones 15"],
+    "expected": "jones 20\nsmith 20\njones 15"
+  },
+  {
+    "title": "Sample Test Case 7",
+    "input": [
+      {
+        "name": "davis",
+        "score": 15
+      },
+      {
+        "name": "davis",
+        "score": 20
+      },
+      {
+        "name": "davis",
+        "score": 10
+      },
+      {
+        "name": "edgehill",
+        "score": 15
+      }
+    ],
+    "sorted": ["davis 20", "davis 15", "edgehill 15", "davis 10"],
+    "expected": "davis 20\ndavis 15\nedgehill 15\ndavis 10"
+  },
+  {
+    "title": "Edge case: draw",
+    "input": [
+      {
+        "name": "kurt",
+        "score": 100
+      },
+      {
+        "name": "kurt",
+        "score": 100
+      }
+    ],
+    "sorted": ["kurt 100", "kurt 100"],
+    "expected": "kurt 100\nkurt 100"
+  }
+]

src/hackerrank/interview_preparation_kit/sort/ctci_comparator_sorting.ts

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+/* eslint-disable class-methods-use-this */
+/* eslint-disable @typescript-eslint/no-unused-vars */
+/* eslint-disable no-useless-constructor */
+/* eslint-disable max-classes-per-file */
+/**
+ * @link Problem definition [[docs/hackerrank/interview_preparation_kit/sort/ctci-comparator-sorting.md]]
+ */
+
+// Start Given code
+
+export class Player {
+  name = '';
+
+  score = 0;
+
+  toString(): string {
+    // Given code
+    return '';
+  }
+
+  comparator(bPlayer: this): number {
+    // Given code
+    return 0 * bPlayer.score;
+  }
+}
+
+// End Given code
+
+export class SortablePlayer extends Player {
+  name = '';
+
+  score = 0;
+
+  constructor(name: string, score: number) {
+    super(name, score);
+
+    this.name = name;
+    this.score = score;
+  }
+
+  toString(): string {
+    return `${this.name} ${this.score}`;
+  }
+
+  comparator(bPlayer: this): number {
+    if (this.score > bPlayer.score) {
+      return -1;
+    }
+    if (this.score < bPlayer.score) {
+      return 1;
+    }
+    if (this.name < bPlayer.name) {
+      return -1;
+    }
+    if (this.name > bPlayer.name) {
+      return 1;
+    }
+
+    return 0;
+  }
+}
+
+export function comparatorSorting(players: SortablePlayer[]): string[] {
+  const sortedPlayers = [...players].sort(
+    (a: SortablePlayer, b: SortablePlayer): number => a.comparator(b)
+  );
+
+  return sortedPlayers.map((player: SortablePlayer) => player.toString());
+}
+
+export function comparatorSortingPrint(players: SortablePlayer[]): void {
+  console.log(comparatorSorting(players)?.join('\n'));
+}
+
+export default { Player, comparatorSorting };