style: use proper spelling

[alxkm]

Fixed few naming and typo issues.

• 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 code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 50.76%. Comparing base (d189c3a) to head (50b9134).

Files with missing lines	Patch %	Lines
...ava/com/thealgorithms/stacks/LargestRectangle.java	0.00%	2 Missing ⚠️
...s/datastructures/lists/MergeKSortedLinkedList.java	0.00%	1 Missing ⚠️
src/main/java/com/thealgorithms/strings/Upper.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5436      +/-   ##
============================================
+ Coverage     50.75%   50.76%   +0.01%     
  Complexity     3138     3138              
============================================
  Files           523      523              
  Lines         15120    15120              
  Branches       2880     2880              
============================================
+ Hits           7674     7676       +2     
+ Misses         7122     7121       -1     
+ Partials        324      323       -1     

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