Simplify kth_factor implementation

[Watagon]

Description

This pull request refactors kth_factor to use Rust iterator methods instead of allocating and manually searching a Vec<i32>.

The implementation iterates over the candidate factors, keeps the values that divide n evenly, selects the (k - 1)th matching value, and returns -1 when no such factor exists. The existing behavior and test cases are preserved.

I would appreciate the maintainers' guidance on two API questions:

1. Should the function explicitly handle k == 0? The current implementation assumes a one-based factor index, and k == 0 currently causes an unsigned subtraction underflow in debug builds.
2. Should the return type remain i32 with -1 indicating that the kth factor does not exist, as in common implementations of this problem, or should it be changed to the more idiomatic Rust type Option<i32>?

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I ran the 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.
  • The command was run and fixed some issues, but it currently fails on 7 pre-existing clippy warnings and they are unfixable.
  • Details in here
• 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 CONTRIBUTING.md and my code follows its guidelines.

Please make sure that if there is a test that takes too long to run ( > 300ms), you #[ignore] that or try to optimize your code or make the test easier to run. We have this rule because we have hundreds of tests to run; If each one of them took 300ms, we would have to wait for a long time.

The clippy warnings

I'm getting the runaround.

The new rule clippy::rest-pattern-accessible-field is causing problems.

An error before the fix:

error: struct destructuring with rest (`..`)
  --> src/compression/huffman_encoding.rs:66:13
   |
66 |             HuffmanNode::Leaf { frequency, .. } | HuffmanNode::Internal { frequency, .. } => {
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/main/index.html#rest_pattern_accessible_field
   = note: `-D clippy::rest-pattern-accessible-field` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::rest_pattern_accessible_field)]`
help: consider explicitly ignoring remaining fields with wildcard patterns (`x: _`)
   |
66 -             HuffmanNode::Leaf { frequency, .. } | HuffmanNode::Internal { frequency, .. } => {
66 +             HuffmanNode::Leaf { frequency, character: _ } | HuffmanNode::Internal { frequency, .. } => {
   |

After fix it following the help:

error: you matched a field with a wildcard pattern, consider using `..` instead
  --> src/compression/huffman_encoding.rs:66:44
   |
66 |             HuffmanNode::Leaf { frequency, character: _ } | HuffmanNode::Internal { frequency, left: _, right: _ } => {
   |                                            ^^^^^^^^^^^^
   |
   = help: try with `Leaf { frequency, .. }`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/main/index.html#unneeded_field_pattern
   = note: `-D clippy::unneeded-field-pattern` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::unneeded_field_pattern)]`

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.88%. Comparing base (2345c66) to head (8093a27).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1069      +/-   ##
==========================================
- Coverage   95.89%   95.88%   -0.01%     
==========================================
  Files         396      396              
  Lines       30440    30431       -9     
==========================================
- Hits        29191    29180      -11     
- Misses       1249     1251       +2     

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[Watagon]

Should I disable clippy::rest-pattern-accessible-field?