equals and hashCode

Lab Java Intermediate 20 points

Create Book(String title, String author) and override equals and hashCode so books with the same title and author are equal. Read n books (title;author) into a HashSet and print how many distinct books there are.

Input

n, then n lines title;author.

Output

The number of distinct books.

Example

Input

4
Dune;Herbert
Emma;Austen
Dune;Herbert
Dune;Someone

Output

Sample input available Sample output available

Editor

Java

Hints

HashSet uses hashCode first, then equals.

Equal objects must have equal hash codes.

Solution explanation

Without these overrides, two separate Book objects are never equal, so the set keeps duplicates.

Show solution

import java.util.HashSet;
import java.util.Objects;
import java.util.Scanner;
import java.util.Set;

class Book {
    final String title, author;

    Book(String title, String author) {
        this.title = title;
        this.author = author;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Book)) return false;
        Book b = (Book) o;
        return title.equals(b.title) && author.equals(b.author);
    }

    @Override
    public int hashCode() {
        return Objects.hash(title, author);
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.nextLine().trim());
        Set<Book> books = new HashSet<Book>();
        for (int i = 0; i < n; i++) {
            String[] p = sc.nextLine().split(";");
            books.add(new Book(p[0].trim(), p[1].trim()));
        }
        System.out.println(books.size());
    }
}

Output

Answer