Ошибка - Если все три числа равны между собой, необходимо вывести все три.
package com.javarush.task.pro.task03.task0305;

import java.util.Scanner;

/*
Три числа
*/

public class Solution {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        int c = scanner.nextInt();
        boolean ab = (a == b);
        boolean ac = (a == c);
        boolean bc = (b == c);
        if (ab && bc && ac)
            System.out.println(a + " " + b + " " + c);
            //else
            //System.out.println("qwe");
            if (ac)
                System.out.println(a + " " + c);
                if (bc)
                    System.out.println(b + " " + c);
                    if (ab)
                        System.out.println(a + " " + b);
                        scanner.close();
    }
}