freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-237-tours-on-a-4-x-...

---
id: 5900f4591000cf542c50ff6c
title: 'Problem 237: Tours on a 4 x n playing board'
challengeType: 5
forumTopicId: 301882
dashedName: problem-237-tours-on-a-4-x-n-playing-board
---

# --description--

Let $T(n)$ be the number of tours over a 4 × $n$ playing board such that:

- The tour starts in the top left corner.
- The tour consists of moves that are up, down, left, or right one square.
- The tour visits each square exactly once.
- The tour ends in the bottom left corner.

The diagram shows one tour over a 4 × 10 board:

<img class="img-responsive center-block" alt="one tour over 4 x 10 board" src="https://cdn.freecodecamp.org/curriculum/project-euler/tours-on-a-4-x-n-playing-board.gif" style="background-color: white; padding: 10px;">

$T(10)$ is 2329. What is $T({10}^{12})$ modulo ${10}^8$?

# --hints--

`toursOnPlayingBoard()` should return `15836928`.

```js
assert.strictEqual(toursOnPlayingBoard(), 15836928);
```

# --seed--

## --seed-contents--

```js
function toursOnPlayingBoard() {

  return true;
}

toursOnPlayingBoard();
```

# --solutions--

```js
// solution required
```
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
+								---
 								id: 5900f4591000cf542c50ff6c
 								title: 'Problem 237: Tours on a 4 x n playing board'
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
+								challengeType: 5
-												fix(curriculum): Added forumTopicId to remaining 1200 challeng… (#36558)


											
										
										
											2019-08-05 16:17:33 +00:00
+								forumTopicId: 301882
-												feat(curriculum): restore seed + solution to Chinese (#40683)

* feat(tools): add seed/solution restore script

* chore(curriculum): remove empty sections' markers

* chore(curriculum): add seed + solution to Chinese

* chore: remove old formatter

* fix: update getChallenges

parse translated challenges separately, without reference to the source

* chore(curriculum): add dashedName to English

* chore(curriculum): add dashedName to Chinese

* refactor: remove unused challenge property 'name'

* fix: relax dashedName requirement

* fix: stray tag

Remove stray `pre` tag from challenge file.

Signed-off-by: nhcarrigan <nhcarrigan@gmail.com>

Co-authored-by: nhcarrigan <nhcarrigan@gmail.com>
											
										
										
											2021-01-13 02:31:00 +00:00
+								dashedName: problem-237-tours-on-a-4-x-n-playing-board
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
+								---
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
+								# --description--
-												fix(curriculum): clean-up Project Euler 221-240 (#42839)

* fix: clean-up Project Euler 221-240

* fix: corrections from review

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
											
										
										
											2021-07-15 12:26:34 +00:00
+								Let $T(n)$ be the number of tours over a 4 × $n$ playing board such that:
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
-												fix(curriculum): clean-up Project Euler 221-240 (#42839)

* fix: clean-up Project Euler 221-240

* fix: corrections from review

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
											
										
										
											2021-07-15 12:26:34 +00:00
+								- The tour starts in the top left corner.
 								- The tour consists of moves that are up, down, left, or right one square.
 								- The tour visits each square exactly once.
 								- The tour ends in the bottom left corner.
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
+								The diagram shows one tour over a 4 × 10 board:
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
-												fix(curriculum): clean-up Project Euler 221-240 (#42839)

* fix: clean-up Project Euler 221-240

* fix: corrections from review

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
											
										
										
											2021-07-15 12:26:34 +00:00
+								<img class="img-responsive center-block" alt="one tour over 4 x 10 board" src="https://cdn.freecodecamp.org/curriculum/project-euler/tours-on-a-4-x-n-playing-board.gif" style="background-color: white; padding: 10px;">
 								$T(10)$ is 2329. What is $T({10}^{12})$ modulo ${10}^8$?
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
+								# --hints--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
-												fix(curriculum): clean-up Project Euler 221-240 (#42839)

* fix: clean-up Project Euler 221-240

* fix: corrections from review

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
											
										
										
											2021-07-15 12:26:34 +00:00
+								`toursOnPlayingBoard()` should return `15836928`.
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
+								```js
-												fix(curriculum): clean-up Project Euler 221-240 (#42839)

* fix: clean-up Project Euler 221-240

* fix: corrections from review

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
											
										
										
											2021-07-15 12:26:34 +00:00
+								assert.strictEqual(toursOnPlayingBoard(), 15836928);
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
+								```
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
+								# --seed--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
+								## --seed-contents--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
 								```js
-												fix(curriculum): clean-up Project Euler 221-240 (#42839)

* fix: clean-up Project Euler 221-240

* fix: corrections from review

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
											
										
										
											2021-07-15 12:26:34 +00:00
+								function toursOnPlayingBoard() {
-												fix: remove Good luck! comment from challenge seed code (#39575)


											
										
										
											2020-09-15 16:57:40 +00:00
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
+								  return true;
 								}
-												fix(curriculum): clean-up Project Euler 221-240 (#42839)

* fix: clean-up Project Euler 221-240

* fix: corrections from review

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>

Co-authored-by: Tom <20648924+moT01@users.noreply.github.com>
											
										
										
											2021-07-15 12:26:34 +00:00
+								toursOnPlayingBoard();
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
+								```
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 18:02:05 +00:00
+								# --solutions--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 22:01:58 +00:00
 								```js
 								// solution required
 								```