Advent of Code 2025

Project Structure

advent_of_code_2025/
├── day_1/
│   ├── main.go
│   ├── input.txt
│   └── README.md
├── day_2/
│   ├── main.go
│   └── input.txt
├── ...
├── utils/
│   └── file_reader.go
├── template/
│   ├── main.go
│   └── input.txt
├── go.mod
└── README.md

Running Solutions

Option 1: Run Individual Days (Recommended)

Each day has its own main.go file. To run a specific day:

# From the project root
cd day_1
go run .

# Or from project root in one command
cd day_1 && go run .

Pros:

• Simple and straightforward
• Each day is independent
• Easy to test and debug individual solutions
• Can run multiple days in parallel in different terminals
• Natural for Advent of Code workflow

Cons:

• Need to navigate to each directory

Option 2: Alternative - Central Runner

If you prefer a central command, create a main.go in the root:

// main.go in project root
package main

import (
    "fmt"
    "os"
)

func main() {
    if len(os.Args) < 2 {
        fmt.Println("Usage: go run . <day>")
        return
    }
    
    day := os.Args[1]
    cmd := exec.Command("go", "run", ".")
    cmd.Dir = filepath.Join(".", fmt.Sprintf("day_%s", day))
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr
    cmd.Run()
}

Then run with: go run . 1

Creating New Days

1. Copy the template directory:

   cp -r template day_2

2. Update the day number in the print statement

3. Add your puzzle input to input.txt

4. Implement your solution

Utility Functions

The utils package contains common functions:

• ReadFileLines(filename string) []string - Reads file lines into a string slice

Add more utilities as needed for:

• Number parsing
• Grid operations
• Graph algorithms
• etc.

Tips

1. Input Files: Always name them input.txt for consistency
2. Testing: Consider adding _test.go files for complex solutions
3. Benchmarking: Use Go's built-in benchmarking for optimization challenges
4. Part 2: Structure your code to easily extend for part 2

Quick Start for New Day

# From project root
cp -r template day_X
cd day_X
# Paste your input into input.txt
go run .