Issue in swapping specific array elements

Question

The following is no homework. I'm just trying to write my own permutation code. I have an idea but I have problems in writing this idea as code.

As example the input is myArray={1,2,3};

Then the output is supposed to be:

I figured out it's possible by switching the first element with second, then switch second with third (however not entirely possible, but I know I need this).

That's why my question is how can I do this in Java?

I have 1 2 3 and I want switch first element with second, so I get 2 1 3. Print this. Now I want switch second element with third, I get 2 3 1, print it. Repeat n! times where n is myArray length.

I tried to do this with the following code but it seems like I'm far away from it :(

public class Test{
    public static void main(String[] args){
        int[] myArray = {1,2,3};

        for(int x=0; x<6; x++){
            for(int i=0; i<myArray.length-1; i++){
                int temp=myArray[i];
                myArray[i]=myArray[i+1];
                myArray[i+1]=temp;
            }
            for(int i=0; i<myArray.length; i++){
                System.out.print(myArray[i]+" ");
            }
            System.out.println("");
        }
    }
}
Output:
2 3 1 
3 1 2 
1 2 3 
2 3 1 
3 1 2 
1 2 3

Have you taken a look at this: stackoverflow.com/questions/2920315/permutation-of-array ? The second answer should help. — quackenator
– quackenator, Commented May 8, 2017 at 20:49

maszter · Accepted Answer · 2017-05-08 21:11:37Z

1

I'm not sure if I understood correctly though.

public static void main(String[] args) {
    int[] myArray = {1, 2, 3};
    for (int i = 0; i < 6; i++) {
        print(myArray);
        int temp = myArray[i % myArray.length];
        myArray[i % myArray.length] = myArray[(i + 1) % myArray.length];
        myArray[(i + 1) % myArray.length] = temp;
    }
}

private static void print(int[] array) {
    for (int anArray : array) {
        System.out.print(anArray + " ");
    }
    System.out.println("");
}

EDIT:

I noticed, there is a wrong order, so it should be better:

public static void main(String[] args) {
    int[] myArray = {1, 2, 3};

    for (int i = 0; i < 6; i++) {
        int idx = i % (myArray.length - 1);
        print(myArray);
        int temp = myArray[idx];
        myArray[idx] = myArray[idx + 1];
        myArray[idx + 1] = temp;
    }
}

edited May 8, 2017 at 21:11

answered May 8, 2017 at 21:03

maszter

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