Java: Display a three-digit number using 1, 2, 3, 4

Last update on May 12 2025 13:17:43 (UTC/GMT +8 hours)

Unique Three-Digit Numbers

Write a Java program to create and display a unique three-digit number using 1, 2, 3, 4. Also count how many three-digit numbers are there.

Pictorial Presentation:

Sample Solution:

Java Code:

import java.util.Scanner;

public class Exercise39 {
    public static void main(String[] args) {
        int amount = 0; // Initialize a counter for three-digit numbers
        
        // Iterate through three nested loops to generate all unique three-digit numbers
        for (int i = 1; i <= 4; i++) {
            for (int j = 1; j <= 4; j++) {
                for (int k = 1; k <= 4; k++) {
                    // Check if 'i,' 'j,' and 'k' are all different (not equal)
                    if (k != i && k != j && i != j) {
                        amount++; // Increment the counter
                        System.out.println(i + "" + j + "" + k); // Print the generated three-digit number
                    }
                }
            }
        }
        
        // Display the total number of generated three-digit numbers
        System.out.println("Total number of the three-digit-number is " + amount);
    }
}

Explanation:

In the exercise above -

• First, the variable 'amount' is initialized to 0. This variable will be used to count the total number of three-digit numbers that meet the criteria.
• The code uses three nested for loops to generate all possible combinations of three digits from 1 to 4.
• The outermost loop iterates through the first digit (i) from 1 to 4.
• The middle loop iterates through the second digit (j) from 1 to 4.
• The innermost loop iterates through the third digit (k) from 1 to 4.
• Within the innermost loop, there is a conditional check if(k != i && k != j && i != j). This condition ensures that 'i', 'j', and 'k' are all distinct digits, meaning they are not equal to each other. This avoids repetition in the generated numbers.
• When a valid combination is found (i.e., three distinct digits), it increments the amount variable, prints the three-digit number in the format 'ijk', and moves on to the next combination.
• Finally, all possible combinations are generated and counted, it prints the total number of three-digit numbers that meet the criteria.

Sample Output:

123                                                                                                      
124                                                                                                      
132                                                                                                      
134                                                                                                      
142                                                                                                      
143                                                                                                      
213                                                                                                      
214                                                                                                      
231                                                                                                      
234                                                                                                      
241  
------
431                                                                                                      
432                                                                                                      
Total number of the three-digit-number is 24 

Flowchart:

For more Practice: Solve these Related Problems:

• Modify the program to generate four-digit unique numbers.
• Find the total number of combinations without repetition.
• Write a program to generate unique numbers using different digits.
• Display only numbers that are prime.

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