refactor: redesign ArrayCombination

[yuvashreenarayanan3]

Related to #5164.

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• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 38.60%. Comparing base (37c2a96) to head (a991feb).

Files	Patch %	Lines
...m/thealgorithms/backtracking/ArrayCombination.java	91.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5181      +/-   ##
============================================
- Coverage     38.60%   38.60%   -0.01%     
  Complexity     2379     2379              
============================================
  Files           516      516              
  Lines         15396    15402       +6     
  Branches       2957     2957              
============================================
+ Hits           5944     5946       +2     
- Misses         9167     9168       +1     
- Partials        285      288       +3     

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[vil02]

Thanks for having a look into this class.

[vil02]

Permutations?

[vil02]

There is nothing bad with n >= 0 and k == 0. Please throw IllegalArgumentException if one of the inputs is negative or n < k.

Please add tests checking if the exception is thrown.

[vil02]

These comments are not too useful.

[vil02]

Why not to express these tests like that:

package com.thealgorithms.backtracking;

import static org.junit.jupiter.api.Assertions.assertEquals;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.Arguments;
import org.junit.jupiter.params.provider.MethodSource;

public class ArrayCombinationTest {
    @ParameterizedTest
    @MethodSource("tcStream")
    void testWithRegularInput(final int n, final int k, final List<List<Integer>> expected) {
        assertEquals(expected, ArrayCombination.combination(n, k));
    }

    private static Stream<Arguments> tcStream() {
        return Stream.of(Arguments.of(4, 0, new ArrayList<ArrayList<Integer>>()), Arguments.of(3, 1, List.of(List.of(1), List.of(2), List.of(3))), Arguments.of(4, 2, List.of(List.of(1, 2), List.of(1, 3), List.of(1, 4), List.of(2, 3), List.of(2, 4), List.of(3, 4))));
    }
}

[vil02]

Wat do you think about

Suggested change

	* Find all combinations of 1..n using backtracking.
	* Find all combinations of 0..n-1 using backtracking.

Clearly this will require changes in the code and tests, but in my opinion it will be much more useful.

[vil02]

This will need an update.

[github-actions]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contribution!