Improve Permutation Implementation

[sozelfist]

Checklist:

• I ran bellow commands using the latest version of rust nightly.
• I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• I ran cargo fmt just before my last commit.
• I ran cargo test just before my last commit and all tests passed.
• I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• I added my algorithm to DIRECTORY.md with the correct link.
• I checked COUNTRIBUTING.md and my code follows its guidelines.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.07%. Comparing base (72dc88f) to head (83ab8fa).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #781   +/-   ##
=======================================
  Coverage   95.07%   95.07%           
=======================================
  Files         309      309           
  Lines       22779    22779           
=======================================
  Hits        21658    21658           
  Misses       1121     1121           

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[sozelfist]

Can you have a look, @vil02?