题解 | 无限长正整数排列字符串

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();

        StringBuilder sb = new StringBuilder();
        int num = 1;

        while(sb.length() < n) {
            sb.append(num);
            num++;
        }

        System.out.print(sb.charAt(n - 1));
    }
}