如何在随机生成的数字数组中打印出重复项的第一个实例？

Question

I've printed 10 random numbers in the range 20-50 while storing them in an array. I'm having trouble getting the duplicates found to work. If there's an instance in the array where there's a duplicate found, I'm trying to print out the position where it was found, not the subscript.

For example:

46

24

46

48

44

20

24

46

44

27

First pair of duplicates were found at positions: 1 and 3

Is the output that I'm trying to achieve if there's duplicates and then the same except "No duplicates were generated." if there wasn't any.

import javax.swing.JOptionPane;
public class sheet11t1
{
    public static void main(String[] args)
    {
        String results = "";
        int numbers[] = new int[10];
        int j;
        for(int i = 0; i < numbers.length; i++)
        {
            numbers[i] = (int) ((Math.random() * 31) + 20);
            results += i + "\n";
        }
        boolean duplicateFound = false;
        for(int i = 0; i < numbers.length - 1 && !duplicateFound; i++)
        {
            for(j = i + 1; j < numbers.length && !duplicateFound; j++)
            {
                if(numbers[i] == numbers[j])
                    duplicateFound = true;
            }
        }
        if(duplicateFound)
                results += "First pair of duplicates were found at positions: " + numbers[i + 1] + " and " + numbers[j + 1];
        else
                results += "No duplicates were generated.";
        JOptionPane.showMessageDialog(null, results);
    }
}

Answer 1

You have to declare both i and j outside your for loops for that approach to work. Also, you print numbers[i+1] and numbers[j+1] , which i guess should be just i+1 and j+1 if you want to print the 1-based positions in the array.

Answer 2

Couple of issues:

• Your if check for whether duplicate is found or not is outside the loop. You should bring them inside.

• Once you set duplicateFound boolean, you never reset it. So you would just get one match only. So you might need to reset that as well.

• You are using number[i+1 or j+1], which should be i+1 or j+1 in your result string formation.

   for (int i = 0; i < numbers.length - 1 && !duplicateFound; i++) { for (j = i + 1; j < numbers.length && !duplicateFound; j++) { if (numbers[i] == numbers[j]) { duplicateFound = true; } if (duplicateFound) { results += "pair of duplicates were found at positions: " + (i + 1) + " and " + (j + 1) + "\\n"; duplicateFound = false; } } } if (results.isEmpty()) { System.out.println("No duplicates were generated."); } else { System.out.println(results); } 

There are further scope of improvement like you don't need duplicateFound variable and no further checks ie if further setting and resetting variable.

Answer 3

What you have to change is the showing of the numbers instead of the index. so for your first loop, change to numbers[i] instead of just i. secondly, In your case of exiting the loop, the i and j are +1, thus when you want to print the index, you just need to specify i and j. below is the codes.

import javax.swing.JOptionPane;
public class example {

public static void main(String[] args) {
    String results = "";
    int numbers[] = new int[10];
    int j = 0;
    int i;
    for(i = 0; i < numbers.length; i++)
    {
        numbers[i] = (int) ((Math.random() * 31) + 20);
        results += numbers[i] + "\n";
    }
    boolean duplicateFound = false;
    for(i = 0; i < numbers.length - 1 && !duplicateFound; i++)
    {
        for(j = i + 1; j < numbers.length && !duplicateFound; j++)
        {
            if(numbers[i] == numbers[j])
                duplicateFound = true;
        }
    }
    if(duplicateFound)
            results += "First pair of duplicates were found at positions: " + (i) + " and " + (j);
    else
            results += "No duplicates were generated.";
    JOptionPane.showMessageDialog(null, results);

}

}

Answer 4

you need to change printing numbers using numbers[i + 1], numbers[j + 1] to i & j values

public static void main(String[] args) {
    String results = "";
    int numbers[] = new int[10];

    for (int i = 0; i < numbers.length; i++) {
        numbers[i] = (int) ((Math.random() * 31) + 20);
        results += (i + 1) + " --- " + numbers[i] + "\n";
    }

    boolean duplicateFound = false;

    int i = 0;
    int j = 0;

    for (; i < numbers.length - 1 && !duplicateFound; i++) {
        for (j = i + 1; j < numbers.length && !duplicateFound; j++) {
            if (numbers[i] == numbers[j]) {
                duplicateFound = true;
            }
        }
    }
    if (duplicateFound) {
        results += "First pair of duplicates were found at positions: " + i + " and " + j;
    } else {
        results += "No duplicates were generated.";
    }

    JOptionPane.showMessageDialog(null, results);
}