BEAKJOON JAVA ALGORITHM #2877(4와7)

https://www.acmicpc.net/problem/2877

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class Main { public static void main(String[] args) throws NumberFormatException, IOException { BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); int num=Integer.parseInt(br.readLine()); int[] a=new int[num+1]; a[0]=4; if(num==2){ a[1]=7; }else if(num>2){ a[1]=7; int j=0; int k=0; for(int i=2;i<num;i++){ if(i%2==0){ a[i]=a[k]*10+a[j]; j++; k++; }else{ a[i]=a[k-1]*10+a[j]; j--; } } } System.out.println(a[num-1]); } } import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class a2877 { public static void main(String[] args) throws NumberFormatException, IOException { BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); int num=Integer.parseInt(br.readLine()); String result=Integer.toBinaryString(num+1); String sum = null; result=result.substring(1); for(int i=0;i<result.length();i++){ if(i==0 && result.charAt(i)=='0'){ sum="4"; }else if(i==0 && result.charAt(i)=='1'){ sum="7"; }else if(result.charAt(i)=='0'){ sum+="4"; }else{ sum+="7"; } } System.out.println(sum); } }