[Bhumit267]

• 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

Description

Fixes an ArrayIndexOutOfBoundsException when computing the 0-th Catalan number (findNthCatalan(0)) in com.thealgorithms.dynamicprogramming.CatalanNumber, and prevents NegativeArraySizeException on negative inputs.

Problem

In CatalanNumber.java, findNthCatalan(int n) initializes catalanArray = new long[n + 1]. For n = 0, the allocated array has length 1 (valid index 0 only). The subsequent line unconditionally sets catalanArray[1] = 1;, throwing an ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 1. By mathematical definition, $C_0 = 1$. Additionally, passing negative values previously triggered NegativeArraySizeException.

Changes

• Added base boundary checks at the beginning of findNthCatalan:
  • Returns 1L for n <= 1 (n == 0 and n == 1).
  • Throws IllegalArgumentException when n < 0.
• Updated Javadoc to document @throws IllegalArgumentException if n is negative.
• Added test cases in CatalanNumberTest for n = 0, n = 1, and n = -1.

Tests

• mvn test -Dtest=CatalanNumberTest (2 tests, 0 failures)
• mvn checkstyle:check (0 violations)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.28%. Comparing base (0a76bf8) to head (392cf58).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #7731      +/-   ##
============================================
- Coverage     82.28%   82.28%   -0.01%     
  Complexity     8412     8412              
============================================
  Files           843      843              
  Lines         26146    26150       +4     
  Branches       5103     5104       +1     
============================================
+ Hits          21514    21517       +3     
  Misses         3841     3841              
- Partials        791      792       +1     

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[alxkm]

Looks good. Thank you for the contribution.