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Fill the Third Array by adding the elements of the First and Second Arrays

I want to generate an array which content would represent a Cartesian product of the two given string-arrays.

In other words, I need to concatenate each String from the first array arr1 with every String from the second array arr2.

Here is my code:

String[] arr1 = {"a", "b", "c"};
String[] arr2 = {"d", "e", "f"};

String[] result = new String[arr1.length * arr2.length];

for (int k = 0; k < result.length; k++) {
    for (int i = 0; i <arr1.length; i++) {
        for (int j = 0; j < arr2.length; j++) {
            result[k] = arr1[i] + arr2[j];
        }
    }
}

System.out.println(Arrays.toString(result));

Current Output:

[cf, cf, cf, cf, cf, cf, cf, cf, cf]

Desired Output:

[ad, ae, af, bd, be, bf, cd, ce, cf]

How can I fix it?

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Answer

You don’t need the very first for-loop, it causes all the values in the resulting array to be overwritten multiple times.

Instead, you need to declare the index k of the resulting array outside the nested loop that generates the Cartesian product of the two given arrays. k should be incremented at each iteration step of the inner loop.

int k = 0;
for (int i = 0; i < arr1.length; i++) {
    for (int j = 0; j < arr2.length; j++) {
        result[k++] = arr1[i] + arr2[j];
    }
}

System.out.println(Arrays.toString(arr3));

Output:

[ad, ae, af, bd, be, bf, cd, ce, cf]
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