Project Euler Java library and solutions

Java programs for Project Euler. Every solution satisfies the one-minute rule. Most solutions complete in less than a few seconds.

To keep with the spirit of Project Euler, each solution after the first 100 problems is encrypted with its corresponding answer. They can be decrypted with the setup steps below.

Level	Problems	Total time to run 25 solutions
1	1 to 25	0.3 seconds
2	26 to 50	0.8 seconds
3	51 to 75	1.8 seconds
4	76 to 100	1.0 seconds
5	101 to 125	0.7 seconds
6	126 to 150	1.1 seconds
7	151 to 175	2.6 seconds
8	176 to 200	2.1 seconds
9	201 to 225	4.4 seconds
10	226 to 250	5.5 seconds
11	251 to 275	25.4 seconds
12	276 to 300	8.9 seconds
13	301 to 325	8.1 seconds
14	326 to 350	10.8 seconds
15	351 to 375	14.0 seconds
16	376 to 400	13.2 seconds
17	401 to 425	31.0 seconds
18	426 to 450	18.6 seconds
19	451 to 475	30.4 seconds
20	476 to 500	25.1 seconds
21	501 to 525	18.5 seconds
22	526 to 550	24.5 seconds
23	551 to 575	55.7 seconds
24	576 to 600	35.3 seconds
25	601 to 625	29.2 seconds
26	626 to 650	37.2 seconds
27	651 to 675	16.4 seconds
28	676 to 700	37.7 seconds
29	701 to 725	26.7 seconds
30	726 to 750	37.9 seconds
31+	751+	In progress!

(Run on Apple M2 Max.)

One-time setup

The solution files are encrypted. To decrypt them, you need a file named answers.txt in the root directory with the following format:

1. answer to Problem 1
2. answer to Problem 2
...

This file does not need to include all the answers, but only solution files with an included answer will be decrypted.

To generate this file automatically for all problems that you've solved on the Project Euler website, run this in the root directory:

$ ./gradlew fetchAnswers

You will be prompted to enter your Project Euler credentials. The task will generate an answers.txt file with answers for all solved problems on your account. It doesn't make any changes to your account.

Now run the following:

$ ./scripts/setup.sh

Files in Git will now be automatically decrypted, and files added to Git will be automatically encrypted.

The setup.sh script must be re-run if any changes are manually made to the answers.txt file.

Running tests

Each solution is a JUnit test that can be run in your IDE, or directly in Gradle:

$ ./gradlew test --tests *p001 // runs the program for Problem 1

To run all tests (takes a few minutes):

$ ./gradlew test

Development

This repository requires Java 8+.

For IntelliJ, run ./gradlew idea and open the project, or use the native Gradle integration.

For Eclipse, run ./gradlew eclipse and then import "Existing Projects into Workspace". You will also need to setup Lombok.