Description

This pull request implements the PageRank algorithm under the graph module.

Algorithm Overview

PageRank is an algorithm used to rank elements in a network based on their structure of incoming links. It computes a probability distribution representing the likelihood that a person randomly clicking on links will arrive at any particular page.

For more details, see the Wikipedia article: https://en.wikipedia.org/wiki/PageRank

Implementation Details

• Genericity: Uses a generic type Node: Hash + Eq + Clone, meaning it can rank nodes of any type (e.g., String, integer types, or custom hashable structures).
• Dangling Nodes: Accurately handles "dangling nodes" (nodes with no outbound edges) by redistributing their rank mass evenly across all nodes in the graph during each iteration.
• Deduplication: Handles duplicate/parallel edges between the same source and destination to prevent artificial weight skewing.
• Convergence: Performs power iteration with an early exit check using an L1 norm difference calculation against a user-defined threshold.
• Testing: Includes 18 tests covering edge cases (such as self-loops, disconnected components, and linear chains) and checking against known analytical results. The entire test suite completes in approximately 0.01s.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I ran below 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 CONTRIBUTING.md and my code follows its guidelines.