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Refine title and update content structure
Updated the title and improved the clarity of the content. Removed performance benchmarks section and adjusted the focus on future developments.
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title: Expanding the C++ Graph Backend - DFS and Bellman-Ford
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date: 2025-10-22 23:25:31 +0530
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categories: [Season of Commits]
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tags: [Week 10]
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---
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This week’s progress focused on extending the C++ graph backend in PyDataStructs with two major algorithmic implementations, Depth-First Search (DFS) and the Bellman-Ford shortest path algorithm. The [PR](https://github.com/codezonediitj/pydatastructs/pull/707) builds upon the existing backend architecture established in earlier commits, further accelerating computation on large graphs while maintaining full compatibility with the Python interface.
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---
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### 1. Adding DFS and Bellman-Ford to the C++ Backend
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The primary goal of this update was to move more core graph algorithms from Python to C++ for improved performance and scalability. With this PR, both **DFS** and **Bellman-Ford** are now available in the C++ backend, enabling faster traversal and shortest-path computations, especially on large or dense graphs.
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---
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### 2. Depth-First Search (DFS) — Iterative, Flexible, and Fast
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The C++ DFS implementation mirrors the behavior of the existing Python version while significantly improving runtime performance.
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Key highlights include:
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- **Iterative stack-based design** — avoids recursion depth limits
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- **Support for both graph types** — adjacency list and adjacency matrix
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- **Custom callback operations** — users can attach operations (like node labeling or early stopping) via function arguments
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- **Full compatibility** — results and traversal order match the Python backend for consistent testing
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This design not only improves efficiency but also provides a framework for extending graph traversal algorithms with user-defined logic, something that will integrate well with future backend expansion (e.g., parallel traversal in LLVM).
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---
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### 3. Bellman-Ford Algorithm — Optimized with SPFA
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The Bellman-Ford shortest path algorithm, implemented as `shortest_paths_bellman_ford_adjacency_list`, was enhanced with the **Shortest Path Faster Algorithm (SPFA)** optimization.
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This approach drastically reduces redundant relaxations on sparse graphs while preserving correctness on graphs with negative weights.
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Key improvements include:
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- **SPFA optimization** for improved average-case performance
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- **Negative weight and cycle detection**
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- **Consistent output format** — returns distances and predecessors identical to Python’s implementation
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- **Optional target node parameter** for partial shortest-path computation
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These features make the C++ backend robust for a wide range of applications from general-purpose graph analytics to low-level algorithm benchmarking.
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---
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### 4. Testing and Validation
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This update includes extensive test coverage to ensure correctness and cross-backend consistency.
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Highlights:
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- Added dedicated C++ backend tests for DFS and Bellman-Ford
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- Verified behavior for graphs with both positive and negative weights
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- Included cycle detection validation in Bellman-Ford
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- Confirmed callback handling in DFS for custom operations
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All tests across Python and C++ backends pass successfully, ensuring stable integration with the existing codebase.
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---
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### 5. The Road Ahead
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With DFS and Bellman-Ford now integrated, the focus shifts toward:
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- **Adding more C++ backend algorithms** — including SCC’s and max flow algorithms
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- **Backend benchmarking suite** — to quantify speedups across graph sizes and structures

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