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Tracks Logic Puzzle Solver: An Exact Constraint Solving Scheme Using Graph Modeling and Mixed Integer Programming

This article introduces an exact solver for the Tracks logic puzzle based on graph modeling and Mixed Integer Programming (MILP), demonstrating how to transform the logic puzzle into a mathematical optimization problem and providing a complete Python implementation along with visualization tools.

逻辑谜题约束求解混合整数规划图论组合优化PythonPuLP算法设计
Published 2026-05-07 20:43Recent activity 2026-05-07 20:50Estimated read 5 min
Tracks Logic Puzzle Solver: An Exact Constraint Solving Scheme Using Graph Modeling and Mixed Integer Programming
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Section 01

Introduction to the Tracks Logic Puzzle Solver Project

This article introduces the josedanielchg/tracks-constraint-solver project, which implements an exact solution for the Tracks logic puzzle using graph modeling and Mixed Integer Programming (MILP). It provides a complete Python implementation, visualization tools, a validator, and datasets, serving as a reference for learning combinatorial optimization, constraint satisfaction problems, and puzzle solving.

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Section 02

Tracks Puzzle Background and Project Overview

Tracks is a grid-based logic puzzle that requires constructing a railway line connecting two terminals, satisfying row and column clues as well as fixed cell constraints. Transforming it into a computational problem involves knowledge in graph theory, combinatorial optimization, and other fields. This project treats Tracks as a graph feasibility problem and achieves exact solving via the MILP method.

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Section 03

Core Methods: Graph Modeling and Technical Architecture

Core Innovations: Abstract the grid into a graph G=(V,E) (cells as vertices, adjacent cells as edges), where a valid route is a connected subgraph satisfying degree constraints, and puzzle rules are converted into graph-theoretic constraints. Technical Components: 1. Puzzle parsing and graph construction (instance parser, graph construction assistant, constraint extractor); 2. MILP solving engine (based on PuLP+CBC, defining edge variables and constraints for connectivity, degree, and clues); 3. Independent validator (verifies connectivity and constraint satisfaction); 4. Visualization (ASCII rendering, Pygame interaction); 5. Datasets and instance generation (manual collection, random generation, experimental screenshot recognition function).

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Section 04

Detailed Mathematical Model

Graph Representation: The grid cell (i,j) corresponds to vertex v_{i,j}, and edges e exist between adjacent cells. Constraints: 1. Terminal constraints (start/end vertices have degree 1); 2. Path constraints (intermediate vertices have degree 2 or vary according to track type); 3. Connectivity constraints (selected edges form a connected subgraph); 4. Clue constraints (number of track segments in rows/columns matches clue values). Optimization Objective: As a feasibility problem, the objective function is set to a constant, seeking a solution that satisfies all constraints.

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Section 05

Project Summary

This project demonstrates how to transform the Tracks puzzle into a rigorous mathematical problem and achieve exact solving using modern optimization tools. With a clear structure and comprehensive documentation, it is a valuable reference for developers and researchers interested in learning combinatorial optimization, constraint satisfaction problems, or puzzle solving.

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Section 06

Application Scenarios and Extension Possibilities

The project's methodology has wide applicability: 1. Path planning (network routing, logistics planning); 2. Constraint satisfaction problems (migrating the MILP framework to other CSPs); 3. Automated puzzle solving (applying the screenshot recognition process to other grid puzzles); 4. Algorithm teaching (case study for graph theory and optimization algorithms).