Nested for loop to compare pairs

Question

My java project is having a little issue here, I simplified it to the following codes. My codes print out:

Index 0 and 1 are pointing to same value. Index 1 and 0 are pointing to same value. Index 3 and 4 are pointing to same value. Index 4 and 3 are pointing to same value.

But what I want is:

Index 0 and 1 are pointing to same value. Index 3 and 4 are pointing to same value.

Because 0 and 1, 1 and 0 are really same pairs, any suggestion?

int[] arr={4,4,5,6,6,};
    
    for(int n=0; n<arr.length; n++)
    {
        for(int m=0; m<arr.length; m++)
        {
            if(arr[n]==arr[m] && n!=m)
            {
                System.out.println("Index "+n+" and "+m+" are pointing to same value.");
            }
        }
    }

This can be done using a single for loop. Is it required to use nested loops? — Kalana, Nov 19 '21 at 04:14

score 3 · Accepted Answer · answered Nov 19 '21 at 04:01

3

If you want to filter out the duplicate ones, change for(int m=0; m<arr.length; m++) to for(int m=n+1; m<arr.length; m++)

answered Nov 19 '21 at 04:01

Max Peng

2,879
1
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this is so clever...how do you get this idea?... and is there any suggestion to improve my problem thinking skills? – ArtStyle.Qwerty Nov 19 '21 at 05:11
Note, you could even do "m – GLJeff Feb 18 '23 at 22:22

score 1 · Answer 2 · edited Nov 19 '21 at 04:09

1

Try this.

int[] arr = {4,4,5,6,6,};

for(int n=0; n<arr.length; n++)
{
    for(int m=0; m<arr.length; m++)
    {
        if(arr[n]==arr[m] && n!=m && m > n || n == 0 && m == 0)
        {
            System.out.println("Index "+n+" and "+m+" are pointing to same value.");
        }
    }
}

edited Nov 19 '21 at 04:09

Dharman

30,962
25
85
135

answered Nov 19 '21 at 04:03

Ricardo Araújo

11
1

thanks for sharing, one more question, I tried m>n, and it prints correct results, so do you think || n == 0 && m == 0 could be redundant> – ArtStyle.Qwerty Nov 19 '21 at 05:32
Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Nov 19 '21 at 07:14

Alexandros Kourtis · Answer 3 · 2021-11-19T04:17:21.973

1

    int[] arr={4,4,5,6,6,};

    for (int n = 0; n < arr.length; n++) {
        for (int m = 0; m < arr.length; m++) {
            if (arr[n] == arr[m] && n != m) {
                if (m > 0 && n + 1 < arr.length) {
                        System.out.println("Index " + n + " and " + m + " are pointing to same value.");
                }
            }
        }
    }

edited Nov 19 '21 at 04:17

answered Nov 19 '21 at 04:09

Alexandros Kourtis

539
2
6
20

score 1 · Answer 4 · answered Nov 19 '21 at 04:16

You can use hash map to get faster.

int[] arr = {4, 4, 5, 6, 6,};
    Map<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < arr.length; i++) {
        int num = arr[i];
        if (map.containsKey(num)) {
            System.out.println("Index " + map.get(num) + " and " + i + " are pointing to same value.");
            map.remove(num);
        } else
            map.put(arr[i], i);
    }

score 0 · Answer 5 · answered Nov 19 '21 at 04:05

You may try to learn some problem solving skills when solving problem like decomposition recursion think back and so on
https://www.youtube.com/watch?v=S47aSEqm_0I
The lecture can teach you a lot.

int[] arr={4,4,5,6,6,};

        for(int n=0; n<arr.length; n++)
        {
            for(int m=n; m<arr.length; m++)
            {
                if(arr[n]==arr[m] && n!=m)
                {
                    System.out.println("Index "+n+" and "+m+" are pointing to same value.");
                }
            }
        }

thanks for sharing this video resource! – ArtStyle.Qwerty Nov 19 '21 at 05:04 — ArtStyle.Qwerty, Nov 19 '21 at 05:04

Nested for loop to compare pairs

5 Answers5