freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-324-building-a-tower.md

---
id: 5900f4b11000cf542c50ffc3
title: 'Problem 324: Building a tower'
challengeType: 5
forumTopicId: 301981
---

# --description--

Let f(n) represent the number of ways one can fill a 3×3×n tower with blocks of 2×1×1. You're allowed to rotate the blocks in any way you like; however, rotations, reflections etc of the tower itself are counted as distinct.

For example (with q = 100000007) :f(2) = 229,f(4) = 117805,f(10) mod q = 96149360,f(103) mod q = 24806056,f(106) mod q = 30808124.

Find f(1010000) mod 100000007.

# --hints--

`euler324()` should return 96972774.

```js
assert.strictEqual(euler324(), 96972774);
```

# --seed--

## --seed-contents--

```js
function euler324() {

  return true;
}

euler324();
```

# --solutions--

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

											
										
										
											2018-09-30 23:01:58 +01:00
+								---
 								id: 5900f4b11000cf542c50ffc3
 								title: 'Problem 324: Building a tower'
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
+								challengeType: 5
-												fix(curriculum): Added forumTopicId to remaining 1200 challeng… (#36558)


											
										
										
											2019-08-05 09:17:33 -07:00
+								forumTopicId: 301981
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
+								---
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
+								# --description--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
+								Let f(n) represent the number of ways one can fill a 3×3×n tower with blocks of 2×1×1. You're allowed to rotate the blocks in any way you like; however, rotations, reflections etc of the tower itself are counted as distinct.
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
+								For example (with q = 100000007) :f(2) = 229,f(4) = 117805,f(10) mod q = 96149360,f(103) mod q = 24806056,f(106) mod q = 30808124.
 								Find f(1010000) mod 100000007.
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
+								# --hints--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
+								`euler324()` should return 96972774.
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
+								```js
 								assert.strictEqual(euler324(), 96972774);
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
+								```
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
+								# --seed--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
+								## --seed-contents--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
 								```js
 								function euler324() {
-												fix: remove Good luck! comment from challenge seed code (#39575)


											
										
										
											2020-09-15 09:57:40 -07:00
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
+								  return true;
 								}
 								euler324();
 								```
-												Feat: add new Markdown parser (#39800)

and change all the challenges to new `md` format.
											
										
										
											2020-11-27 19:02:05 +01:00
+								# --solutions--
-												feat(challenge-md): Add initial markdown challenge files

											
										
										
											2018-09-30 23:01:58 +01:00
 								```js
 								// solution required
 								```