PrayHee

import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner key = new Scanner(System.in);
		
		int A = key.nextInt();
		int B = key.nextInt();
		System.out.println(A-B);
		
	}

}

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in); //스캐너 생성
		String str = sc.next(); //문자를 받아서 str 변수에 입력
		char[] arr = str.toCharArray(); //str 변수를 arr 배열 값에 넣음
		int stop = sc.nextInt(); //멈출 int 변수를 생성
		char chStop = 0; //출력할 char 변수 생성
		
		for (int i = 0; i < stop; i++) {
			chStop = arr[i];
		}
		System.out.println(chStop);
	}
}

주석문 확인 ~~

package JavaTestBackJoon;

import java.util.Arrays;
import java.util.Scanner;

public class B3052 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int[] arr = new int[10];
		int cnt = 0;

		for (int i = 0; i < arr.length; i++) {
			arr[i] = sc.nextInt();
			arr[i] %= 42;
//			System.out.print("반복문 " + arr[i] + " ");
		}
		Arrays.sort(arr);
		for (int i = 0; i < arr.length - 1; i++) {
			if (arr[i] != arr[i + 1]) {
				cnt++;
//				System.out.println("cnt는 " + cnt);
			}
		}
		System.out.println(cnt+1);
	}
}