[백준] 1790번 : 수 이어 쓰기 2 - Java(자바)

https://www.acmicpc.net/problem/1790

import java.util.Scanner;
public class Main {
    static long count(long t){
        long num=1;
        for(int i=0;i<t;i++){
            num*=10;
        }
        return num;
    }
    public static void main(String args[]) {
        Scanner s=new Scanner(System.in);
        int n=s.nextInt();
        int k=s.nextInt();
        int t=1;
        long num=0;
        int r=0;
        int e=0;
        while(true){
            long max=(count(t)-count(t-1))*t;
            
            if(num+max>=k){
                k-=num;
                r=k/t;
                e=k%t;
                n-=r;
                break;
            }
            num+=max;
            n-=count(t)-count(t-1);
            t++;
        }
        r+=count(t-1)-1;
        if(n<0 || n==0 && e!=0) System.out.print("-1");
        else if(e==0){
            String m=r+"";
            System.out.format("%c",m.charAt(m.length()-1));
        }
        else{
            r+=1;
            String m=r+"";
            System.out.format("%c",m.charAt(e-1));
        }
    }
}