Unique Number in Java Program

The number will be unique if it is positive integer and there are no repeated digits in the number. In other words, a number is said to be unique if and only if the digits are not duplicate. For example, 20, 56, 9863, 145, etc. are the unique numbers while 33, 121, 900, 1010, etc. are not unique numbers. In this section, we will create Java programs to check whether the number is unique or not.

There are the following ways to check the number is unique or not:

By Comparing Each Digit Manually
Using String
Using Array

By Comparing Each Digit Manually

There are the following steps to check number is unique or not:

Read a number from the user.
Find the last digit o the number.
Compare all digits of the number with the last digit.
If the digit found more than one time, the number is not unique.
Else, eliminate the last digit of the number.
Repeat steps 2 to 5 until the number becomes zero.

UniqueNumberExample1.java

import java.util.Scanner;
public class UniqueNumberExample1
{
public static void main(String args[])
{
int r1, r2, number, num1, num2, count = 0;
Scanner sc = new Scanner(System.in);
System.out.print("Enter the number you want to check: ");
//reading a number from the user
number = sc.nextInt();
//num1 and num2 are temporary variable
num1 = number;
num2 = number;
//iterate over all digits of the number
while (num1 > 0)
{
//detrmins the last digit of the number    
r1 = num1 % 10;
while (num2 > 0)
{
//finds the last digit
r2 = num2 % 10;
//comparing the last digit
if (r1 == r2)
{
//increments the count variable by 1    
count++;
}
//removes the last digit from the number
num2 = num2 / 10;
}
//removes the last digit from the number
num1 = num1 / 10;
}
if (count == 1)
{
System.out.println("The number is unique.");
}
else
{
System.out.println("The number is not unique.");
}
}
}

Output 1:

Enter the number you want to check: 13895
The number is unique.

Output 2:

Enter the number you want to check: 11100
The number is not unique.

Output 3:

Enter the number you want to check: 10000
The number is not unique.

Using String

Using String, we can also check the number is unique or not. We use the charAt() method of the String to compare each digit of the string.

UniqueNumberExample2.java

import java.util.*;
public class UniqueNumberExample2
{
public static void main(String args[] )
{
Scanner sc=new Scanner(System.in);
System.out.print("Enter the number you want to check:");
//reading an integer from the user
int number=sc.nextInt();
//converts integer data type into string
String str= Integer.toString(number); 
//determines the length of the string
int length=str.length();
int flag=0, i, j;
//loop checks the digits are repeated or not
for(i=0;i<length-1;i++)
{
for(j=i+1;j<length;j++)
{
//comparing each digit, if digits are repeated the number is not unique     
if(str.charAt(i)==str.charAt(j)) 
{ 
flag=1;
break; 
}
}
}
//if flag is equal to zero the number is unique
if(flag==0)
System.out.println("The number is unique.");
else
System.out.println("The number is not unique.");
}
}

Output 1:

Enter the number you want to check: 9876
The number is unique.

Output 2:

Enter the number you want to check: 1010
The number is not unique.

Output 3:

Enter the number you want to check: 200
The number is not unique.

In the above program first, we convert the number variable into String by using the toString() method. After that, we determine the length of the string using the length() method.

We have used two for loop (inner and outer) that iterate over the number. Inside the if statement, for each iteration, we have compared the digits by using the charAt() method. If both digits are the same, the break statement breaks the execution of the program and prints the number is not unique, else prints the number is unique.

Using Array

We can also use an array to check the number is unique or not. In this method, we find all the digits of the number and store it into an array. After that, compare the values of all the indexes with each other. If the values are the same, the number is not unique. Remember that before comparing all the indexes we required to declare the size of the array (number of digits).

UniqueNumberExample3.java

import java.util.Scanner;
public class UniqueNumberExample3
{
//static method that checks the number is unique or not
public static boolean isUniqueNumber(int number) 
{
//count the number of digits in a number
int digits = countDigits(number);
//declaring and creating an array of digits
int[] arr = new int[digits];
for(int i=0; i<digits; i++) 
{
//determines the last digits and adds it to the ith position
arr[i] = (int)number%10;
//removes the last digit
number = number/10;
}
//compares array elements
for(int i=0; i<digits; i++) 
{
for(int j=0; j<digits; j++) 
{
//returns true if both conditions are true    
if(i!=j && arr[i]==arr[j])
return false;
}
}
return true;
}
public static int countDigits(int number) 
{
int count = 0;
//executes until the condition becomes false
while(number != 0) 
{
//increments the variable count by 1
count++;
//removes last digits
number= number/10;
}
return count;
}
public static void main(String args[]) 
{
//declare variables
int number = 0;
boolean result = false;
//create Scanner class object to take input
Scanner scan = new Scanner(System.in);
System.out.print("Enter the number you want to check: ");
//reading an integer from the user
number = scan.nextInt();
//invoking the method and parsing the number to be check
result = isUniqueNumber(number);
if(result)
System.out.println(number +" is a unique number.");
else
System.out.println(number +" is not a unique number.");
}
}

Output 1:

Enter the number you want to check: 898
898 is not a unique number.

Output 2:

Enter the number you want to check: 201
201 is a unique number.

Output 3:

Enter the number you want to check: 700
700 is not a unique number.

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