Created a Permutation Function in the Recursion package. Closed the issue #7322

[trynafind-sumanyu]

Issue #7322

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new algorithms include a corresponding test class that validates their functionality.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.55%. Comparing base (2616e09) to head (a8a8e13).

Files with missing lines	Patch %	Lines
...java/com/thealgorithms/recursion/Permutations.java	92.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7412      +/-   ##
============================================
+ Coverage     79.54%   79.55%   +0.01%     
- Complexity     7178     7186       +8     
============================================
  Files           798      799       +1     
  Lines         23467    23492      +25     
  Branches       4617     4621       +4     
============================================
+ Hits          18666    18690      +24     
- Misses         4055     4056       +1     
  Partials        746      746              

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[DenizAltunkapan]

@trynafind-sumanyu there exists another permutation class: https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/backtracking/Permutation.java
Whats the difference between these?

[trynafind-sumanyu]

Hey @DenizAltunkapan,

I wasn’t aware that a permutation implementation already existed under the backtracking package, as the issue specifically referenced the recursion package, where no such file was present. Based on that, I proceeded with adding a new implementation there.

Additionally, I introduced handling for duplicate elements to ensure that only unique permutations are generated. This behavior was not present in the existing backtracking/Permutation.java implementation.

Please let me know if you’d prefer aligning this with the existing implementation or consolidating the changes.

[DenizAltunkapan]

Hey @DenizAltunkapan,

I wasn’t aware that a permutation implementation already existed under the backtracking package, as the issue specifically referenced the recursion package, where no such file was present. Based on that, I proceeded with adding a new implementation there.

Additionally, I introduced handling for duplicate elements to ensure that only unique permutations are generated. This behavior was not present in the existing backtracking/Permutation.java implementation.

Please let me know if you’d prefer aligning this with the existing implementation or consolidating the changes.

@trynafind-sumanyu You can align these in the existing implementation. Just make sure that there aren't any duplicates. Thank you and sorry for the late reply : )

[prashantpiyush1111]

Overall the implementation is well-structured with good
test coverage. However, the main concern is the duplicate
class — please align with the existing
backtracking/Permutation.java as suggested by
@DenizAltunkapan. Please address all inline comments. 🙌

[prashantpiyush1111]

As mentioned by @DenizAltunkapan, a Permutation class already
exists at backtracking/Permutation.java. Please align your
unique permutations logic into the existing implementation
instead of creating a separate class.

[prashantpiyush1111]

HashSet relies on hashCode() and equals() for deduplication.
For custom objects that don't override these methods,
duplicates may not be detected correctly.
Consider documenting this assumption in JavaDoc or
using explicit comparison instead.

[prashantpiyush1111]

Test file name should be PermutationsTest.java not
Permutations.java — as per TheAlgorithms naming convention.

[prashantpiyush1111]

Private constructor is not tested — this is causing
2 uncovered lines in Codecov.

Add:
@test
void testConstructorThrowsException() {
assertThrows(UnsupportedOperationException.class, () -> {
var constructor = Permutations.class.getDeclaredConstructor();
constructor.setAccessible(true);
constructor.newInstance();
});
}