Days Between Two Dates

java.time was added in Java 8.

/*
 * Problem : Count the days between two dates.
 * Input   : Two dates.
 * Output  : The number of days.
 * Approach: Use the date library.
 * Time    : O(1)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static long solve(String a, String b) {
        // Step 1: LocalDate is the date class of java.time (Java 8). parse reads the text YYYY-MM-DD.
        java.time.LocalDate first = java.time.LocalDate.parse(a);
        java.time.LocalDate second = java.time.LocalDate.parse(b);

        // Step 2: ChronoUnit.DAYS.between counts the days from the first date to the second date.
        return java.time.temporal.ChronoUnit.DAYS.between(first, second);
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String a = scanner.next();
        String b = scanner.next();
        System.out.println(solve(a, b));
    }
}