Last update: 2014-12-09

My Problems (SPOJ)

Classical:

1. Ancient Aliens (2013-06-01)
2. Farmer Joe (2013-06-01)
3. One Good Base Deserves Another (2013-06-01)
4. A Kleene Implementation (2013-06-01)
5. Peculiar Permutivores (2014-03-29)
6. Some Sums (2014-06-07)
7. Distinct Viewpoints (2014-09-27)

Tutorial:

1. The Brain-Folk Computer (2013-06-01)
2. Permutation Cycle Decomposition (2014-03-29)

SHORTEN Main:

1. The Brain-Folk Computer (2013-07-28)

BSCPROG Cpttrn:

1. Cross Pattern (Act 1) (2014-01-12)
2. Cross Pattern (Act 2) (2014-01-12)

My Problems (Elsewhere)

Mathalon:

1. How many zeros 2 (2011-12-27) [screenshot in case server is down]

Anarchy Golf:

1. Gizoogle (2014-02-16)
2. Circlify (2014-03-01)
3. Anarchic Antarctic Scene (2014-03-02)
4. The Fool on the Hill (2014-03-12)
5. Searching for Paul McCartney (2014-03-13)
6. Making Molehills out of Mountains (2014-03-13)
7. Permutation Cycles (2014-03-26)
8. Permutation Composition (2014-04-11)
9. The Logfather (2014-05-29)
10. Ant Paths (2014-07-16)
11. Stars and Bars (2014-08-18)
12. Enumerate Compositions (2014-11-11)
13. Polyominoes (2014-12-01)

Recommended Brainf**k Problems

"I am endeavoring, ma'am, to construct a mnemonic memory circuit using stone knives and bearskins." — Spock

Some useful links:

• Wikipedia article
• Icemens' tutorial on YouTube
• Daniel B. Cristofani's suggestions for intermediate BF programmers
• Alex Pankratov's bff, the BF interpreter used on SPOJ
• Thomas Cort's BFI, the BF interpreter used on Anarchy Golf

This section is inspired by Tjandra's excellent list of brainf**k solvable problems. His list includes some problems that mine doesn't, and vice versa.

Note: where a problem code is given, hover the mouse over it to see the problem title.

Problems where only BF is allowed: (Classical: 16) BFBASE, BFCC, BFDIV, BFGCD, BFMUL, BFONP, BFPRMCYC, BFREGEX1, BFROTATE, BFTAB, BFTRI, CRYPTO2, FAST_BF, FCTRL5, MULTIPLY, SORTING (Challenge: 9) BFBIGTHN, BFMODULO, BFSTR1, BFWRITE, FAST_BF2, HS09BF, LIB, MODULUS2, TSET (Tutorial: 3) BFBINADD, MB2, QWERTY02 (Partial: 1) BGEEK (SHORTEN: 7) BFBIGTHN, BFBINADD, BF_PRIME, BF_SHORT, MAXMINBF, MB2, ODDBF (Polish SPOJ Hard: 3) AL_18_07, AVER_BF, MAXMINBR (Polish SPOJ Medium: 1) BFTRIANG (Polish SPOJ Easy: 1) OSTBR (Polish SPOJ Challenge: 2) BFEVIL, ODDBF

Problems where only BF and (Whitespace and/or Intercal) are allowed: (Classical: 5) ADITYA13, CRYPTO3, EDIT1, GALAXY, SBSTR1

Below is a list of selected problems that can be solved with BF even though they weren't designed for it. They are sorted by category, then chronologically.

Classical:

1. Factorial
2. Adding Reversed Numbers
3. Street Parade
4. To and Fro
5. Ws Cipher
6. Java vs C ++
7. A Game with Numbers
8. Revenge of the squares
9. With a Pit of Death
10. Run length encoding

Challenge:

1. Kamil
2. Plant a Christmas Tree
3. Digits of Pi
4. Digits of e
5. Japan Crossword
6. X-Words
7. Size Contest
8. Shortest Superstring
9. Prime checker
10. Digits of SQRT(2)
11. Nop
12. Polybius square
13. Reverse the Input
14. Christmas Tree
15. Automatic Brainf##k Code Generator (Shortening AI)

Tutorial:

1. Run Length Decoding
2. University Employees
3. Adding two numbers
4. Look and Say
5. Mirrored Pairs
6. Harry and big doughnuts
7. The Quine
8. Arabic and English
9. Plus Within a diamond
10. Vowels
11. Beautiful Numbers
12. Fibonacci Easy
13. Add
14. Problems 2: DIV, MOD and IF
15. Problems 3: For Fun Sequence
16. Problems 5: String

SHORTEN Main:

1. Plant a Christmas Tree
2. Size Contest
3. Fibonacci numbers
4. Next permutation
5. Zeros of factorial
6. Positional notations
7. Polybius square
8. Morse code
9. Reverse Polish notation
10. Street parade (challenge)
11. Look and say (challenge)
12. Anagram (challenge)
13. Printing triangle
14. Adding reversed numbers (challenge)
15. Reverse the Input
16. Revenge of the squares
17. Different sums
18. Secret code

SHORTEN Printing:

1. Foreword to the Fables
2. Yin Yang
3. Hello Kitty (challenge)
4. No comment
5. Mundial 2014

SHORTEN Tutorial:

1. Kamil
2. Reverse order
3. H Function

Polish SPOJ Hard:

1. Precz z komentarzami!

Polish SPOJ Medium:

1. Gray code
2. Podzbiory
3. Sumy
4. Enigma w wersji nieco mniej light

Polish SPOJ Easy:

1. Dwie cyfry silnii
2. Flamaster
3. Tablice
4. StringMerge
5. ROL
6. Zadanie próbne
7. Wiatraczki
8. Połowa
9. Test 3
10. Transponowanie macierzy
11. Parzyste nieparzyste
12. Tabelki liczb
13. Zliczacz liter
14. Pesel
15. ROL (k)
16. Spacje
17. Tagi HTML
18. Szyfr Cezara
19. Samolot
20. Godzina chaosu
21. Odwracanie wyrazów
22. Zliczanie liczb i wyrazów
23. Zliczanie linii
24. Zliczanie wystąpień (kody ASCII)
25. Wycinanie literek
26. Kabalistyczny zapis daty
27. Szyfrowanie ROT13
28. Harry and big doughnuts
29. PTwPZ KWIX
30. XV
31. Enigma w wersji light
32. Sekretny kod
33. Enigma w wersji light po raz kolejny
34. Mundial 2014
35. Małe szyfrowanko
36. Skalowanie

Polish SPOJ Challenge:

1. Kompresor prac domowych

BSCPROG Cpttrn:

1. Character Patterns (Act 1)
2. Character Patterns (Act 2)

Anarchy Golf:

1. delete blank lines
2. even lines
3. sort characters
4. Fibonacci Numbers
5. delete last line
6. swap lines
7. rotate lines
8. transpose lines
9. FizzBuzz
10. infix to postfix
11. reverse lines
12. maze solving
13. Quine
14. Look and say
15. Palindromic Quine
16. rot13
17. Drop first line
18. stratum
19. double back lines
20. Count asterisks
21. Carriage no return
22. add_sub_brainfuck_code
23. long decimal
24. FibBuzz
25. BuzzFib
26. Reverse Bits FIXED
27. A plus B problem
28. pretty maze
29. Next Permutation
30. Rotation
31. fill dots
32. Fixed Rows
33. Maze
34. All Factors
35. All Factors 2
36. Bitwise Counting
37. Stagger Encode FIXED
38. Jump Numbers
39. String Assembly
40. Accumulated value
41. Sum of all permutations
42. Harshad numbers
43. sum of divisors of n
44. identity matrix
45. Every third line
46. Space Reversal
47. Not Quine
48. Widen words
49. Enclose in HTML
50. Inverse Quine
51. yesno
52. Some Pattern FIXED
53. rotate counterclockwise
54. eight hundred
55. count up digits
56. Anarchic Antarctic Scene
57. Making Molehills out of Mountains
58. Permutation Cycles
59. Numbers Cap
60. Number Sequence MEDIUM
61. Stars and Bars
62. squeeze FIXED
63. ascii diagonal
64. PATH
65. What have I got in my POCKET
66. Ordered text permutations
67. Mail merge
68. Swap The Characters
69. Basic Brainfuck Code Optimization
70. Enumerate Compositions

Frequently Asked Questions (Comments)

This section is experimental. :) For some reason, many of the same questions get asked over and over again in comments. Maybe this FAQ can help with that a little.

Q: plz chek my cd....solvd d problem but d site sez WRONG ANS... plzzz hlppp

A: Please use English! Aside from aesthetic concerns, this will make it easier for others to understand you. Note that many users on SPOJ are not native English speakers (and might be using tools like Google Translate).

Q: Somebody please check my code, submission ID 12345678.

A: Only you, the problem setter, and admins can see your code.

Q: Admins please check my code, submission ID 12345678.

A: The admins are too busy to get involved in such matters, and it's not their job.

Q: Problem setter please check my code, submission ID 12345678.

A: Debugging is part of the problem solving process. As you gain experience, you will naturally get better at preventing bugs and tracking them down when they occur.

It's not the problem setter's job to debug the code of all users wishing to solve their problems. Some problem setters may have time and motivation to help with many such requests, but that goes beyond their responsibility, and you should be very thankful if they choose to do so for you! (The problem setter's responsibility is to make sure that his/her published problems are written clearly, have correct and preferably strong test data, reasonable constraints, etc.)

Also consider that such a request for help is generally of little value to anybody except yourself. In some cases there may be other comments that are more useful for everyone to read, and by publishing your comment, you push those useful comments down the page or onto the next page of comments, making them less easily visible.

There is a special case when it's very reasonable to ask for the problem setter to check your submission: the case when you have reason to believe there is an error with the judging or the judge data. If you plan to make such a claim, you should of course test your reasoning and your code very thoroughly first. Errors sometimes occur in recently published problems with few or no solvers, and only rarely do they occur in problems that are older and/or have many solvers.

If the problem has been solved by many people, then there's a decent chance you'll be able to find help on the forum. Before posting on the forum, be sure to read TripleM's post Read this before posting! and Leppy's post PLEASE USE CODE TAGS.

Even for hard problems with few solvers, asking the problem setter for help should be a last resort. You might get a better response if you make clear that you went to reasonable lengths to debug your own code, e.g. maybe you wrote a slow brute force solution for smaller cases to compare against the proposed faster solution, and after checking many cases you were unable to find a case where your faster code fails.

Q: My code ran fine until "Running... (17)" and then failed. Does test file #17 contain any tricky cases?

A: You have misunderstood the way judging works. The judge does not halt on first failure, so if there are many test files then you may very well see "Running... (17)" even though your code failed on the very first one.

Q: Please give additional test cases.

A: Please don't ask for spoilers in the comments section.

Everything to understand and solve the problem should already be included in the problem statement. If you think additional cases are needed to help understand the problem, then you should rather state specifically what you think is unclear in the problem statement.

This type of question could be appropriate for the forum. See also the answer to this question regarding debugging help.

Q: I'm not seeing how to solve the problem. Please give a hint.

A: Please don't ask for spoilers in the comments section.

Sometimes vague hints can be OK, but this can be hard to discern, and the safest way is simply not to tell or ask for any hints. While you may enjoy having answers handed to you, there are other people who enjoy finding things out on their own, and what you are requesting could ruin their enjoyment. If you saw someone solving a crossword puzzle, would you look over their shoulder and shout answers and hints at them? I should hope not. Please be respectful of other users.

This type of question could be appropriate for the forum. Note that giving a good hint (one that leads you in the right direction but doesn't give too much away) can be hard for some problems. See also the answer to this question regarding debugging help.

Q: The time limit is 5s, but there are accepted solutions that take more than 5s to run. How is that possible?

A: This usually means that there are multiple test files, each with a limit of 5s, and the running time you see is actually the sum of times over all test files. More details about time limits can be found in the Memory and time constraints for solutions section of the official SPOJ tutorial for new (and not only new) users.

It could also mean that the problem setter lowered the time limit at some point and then neglected to rejudge users' submissions, but that's very rare.