[백준 알고리즘] 단계별로 풀어보기 1단계 JAVA

 

백준 알고리즘 문제 단계별로 풀어보기를 시작하려 한다. 1단계부터 차근차근 문제 풀며 나오는 개념을 정리 start! 

 

 

https://www.acmicpc.net/step/1

입출력과 사칙연산 단계

 

 

📑 1. Hello World ( 2557)

 

public class Main {
    public static void main(String args[]){
        System.out.println("Hello World!");
    }
}

 

 

📑 2. A+B (1000)

 

Scanner sc = new Scanner(System.in);

int A = sc.nextInt();
int B = sc.nextInt();
System.out.println(A+B);

 

조건에 보면 (0<A, B<10)이 나와있길래 조건을 줬는데 답변 찾아보면 굳이 주지 않아도 정답으로 체크된다. 

 

package step1;

import java.util.Scanner;

public class Q2_1000 {

	public static void main(String args[]) {
		
		Scanner sc = new Scanner(System.in);
		
		int A = sc.nextInt();
		int B = sc.nextInt();
		
		while(true) {
		if(A>0 && B<10) {
			System.out.print(A+B);
			break;
		}else {
			A = sc.nextInt();
			B = sc.nextInt();
		}
		}
		
		
		
		sc.close();
	}
}

 

 

 

📑 5. A/B (1008)

 

 처음에 float 했더니 틀렸다.  double로 바꾸면 된다! 

 

package step1;

import java.util.Scanner;

public class Q5_1008 {

	public static void main(String args[]) {
		
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		
		
		System.out.println((double)a/b);
		
	}
}

 

 

 

 

📑 6. 사칙연산 (10869)

 

package step1;

import java.util.Scanner;

public class Q6_10869 {

	public static void main(String[] args) {


		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		
		System.out.println(a+b);
		System.out.println(a-b);
		System.out.println(a*b);
		System.out.println(a/b);
		System.out.println(a%b);
		
		sc.close();
	}

}

 

 

📑 7. ??!(10926)

 

<Scanner 사용>

package step1;

import java.util.Scanner;

public class Q7_10926 {


	public static void main(String[] args) {


		Scanner sc = new Scanner(System.in);
		String name = sc.next();
		
		System.out.println(name + "??!");
	}
}

 

 

<BufferedReader 사용>

package step1;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Q7_10926 {


	public static void main(String[] args) throws IOException{


		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String name = br.readLine();
		System.out.println(name + "??!");
	}
}

 

 

 

 

📑 10. 빈 칸에 들어갈 수는?

 

package step1;

import java.util.Scanner;

public class Q10_2588 {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		String A = sc.next();
		String B = sc.next();
		int multipl = 0;
		
		for(int i = 2; i>=0; i--) {
			
			int subB = Integer.parseInt(B.substring(i, i+1)); 
			multipl = Integer.parseInt(A) * subB;
			System.out.println(multipl);
		}
		
		System.out.println(Integer.parseInt(A) * Integer.parseInt(B));
		
		sc.close();
		
		
	}

}

 

 

String의 substring을 이용해서 문자열 자릿수를 자르는 방식을 이용했다. 다른 정답들은 다음과 같다. 

 

 

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        int A = Integer.parseInt(br.readLine());
        String B = br.readLine();
        
        char[] arr = B.toCharArray();
        
        System.out.println(A * (arr[2] - '0'));
        System.out.println(A * (arr[1] - '0'));
        System.out.println(A * (arr[0] - '0'));
        System.out.println(A * Integer.parseInt(B));
    }
}

 

 

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class Main{
    public static void main(String args[])throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int a = Integer.parseInt(br.readLine());
        int b = Integer.parseInt(br.readLine());
      
        int n100 = b/100;
        int n10 = b/10- n100*10;
        int n1 = b - n100*100 - n10*10;
      
        int m1 = a * n1;
        int m2 = a * n10;
        int m3 = a * n100;
        
        System.out.println(m1);
        System.out.println(m2);
        System.out.println(m3);
        System.out.println(m1+m2*10+m3*100); 
    }
}