Given a number, return the count of numbers having non-repeating digits till that number starting from 1?

Question

Let's assume it means two consecutive digits can not be the same. If it means that all digits are unique the logic is very similar as well.

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

class solution {


 public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int no = scan.nextInt();
        int count = 0;
        for(int i=1;i<=no;i++)
        {
          String a = Integer.toString(i);
          char[] b =a.toCharArray();

          Arrays.sort(b);
          String x = new String(b);
      //    System.out.println("Sorted array:"+x);
          int flag = 0;
          if(a.length()>1)
        {
          for(int j=1;j<a.length();j++)
          {
            //System.out.println(b[j-1]+"=="+b[j]);
            if( (b[j-1]==b[j]))
            {
              flag =1;
            //  System.out.println("Has Repeated Numbers!");
              break;
            }
          }
        }
          if(flag == 0)
          {
            count++;
          //  System.out.println("count:"+count+" --> "+"No:"+a);
          }
        }
        System.out.println("Final Count:"+count);
   }
}

INPUT 1: 3456

OUTPUT 1: 2562

INPUT 2: 22

OUTPUT 2: 20

INPUT 3: 7

OUTPUT 3: 7

INPUT 4: 100

OUTPUT 4: 90

INPUT 5: 37

OUTPUT 5: 34

My code satisfies input test cases from 2 to 5 but not for input 1. I understand that every digit should be unique in a number. Can anyone say where I have done my mistake in my logic from the code for input1?

Answer 1

Use regex!

int count = IntStream.rangeClosed(1, n)
    .mapToObj(Integer::toString)
    .filter(s -> s.matches("(?!.*?(.)\\1).*"))
    .count();

Answer 2

What gone wrong in my logic is here I assumed no two digits can be the same , but the looking keenly on the problem statement it says no two consecutive digits can not be the same .

Here is the working code for the above input test cases. Thanks to Paul Hankin for pointing out.

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

class solution {


 public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int no = scan.nextInt();
        int count = 0;
        for(int i=1;i<=no;i++)
        {
          String a = Integer.toString(i);
          char[] b =a.toCharArray();
          int flag = 0;
          if(a.length()>1)
        {
          for(int j=1;j<a.length();j++)
          {
            //System.out.println(b[j-1]+"=="+b[j]);
            if( (b[j-1]==b[j]))
            {
              flag =1;
            //  System.out.println("Has Repeated Numbers!");
              break;
            }
          }
        }
          if(flag == 0)
          {
            count++;
            //System.out.println("count:"+count+" --> "+"No:"+a);
          }
        }
        System.out.println(count);
   }
}