Exercism v3 launches on Sept 1st 2021. Learn more! ๐๐๐

Published at Jul 13 2018
·
0 comments

Instructions

Test suite

Solution

Compute Pascal's triangle up to a given number of rows.

In Pascal's Triangle each number is computed by adding the numbers to the right and left of the current position in the previous row.

```
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
# ... etc
```

Refer to the Exercism CoffeScript page for getting started with CoffeeScript.

In order to run the test, you can run the test file from the exercise directory:

```
jasmine-node --coffee .
```

Pascal's Triangle at Wolfram Math World http://mathworld.wolfram.com/PascalsTriangle.html

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

```
Pascal = require './example.coffee'
describe 'Pascal', ->
it 'with one row', ->
arr = new Pascal(1)
expect(arr.array).toEqual [[1]]
xit 'with two rows', ->
arr = new Pascal(2)
expect(arr.array).toEqual [[1], [1,1]]
xit 'with three rows', ->
arr = new Pascal(3)
expect(arr.array).toEqual [[1], [1,1], [1,2,1]]
xit 'with four rows', ->
arr = new Pascal(4)
expect(arr.array).toEqual [[1], [1,1], [1,2,1], [1,3,3,1]]
xit 'with five rows', ->
arr = new Pascal(5)
expect(arr.array).toEqual [[1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1]]
xit 'should equal 20th row', ->
arr = new Pascal(20)
expect(arr.array[19]).toEqual [1, 19, 171, 969, 3876, 11628, 27132, 50388, 75582, 92378, 92378, 75582, 50388, 27132, 11628, 3876, 969, 171, 19, 1]
```

```
class Pascal
constructor:(@rows) ->
@array = []
for r in [0..@rows-1]
if r == 0
@array.push [1]
else
prevRow = @array[r-1]
working = [1]
if (prevRow.length > 1)
for i in [0..(prevRow.length-1)]
p = prevRow[i] ? 0
n = prevRow[i+1] ? 0
working.push p + n
else
working.push 1
@array.push working
module?.exports = Pascal
```

A huge amount can be learned from reading other peopleโs code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

Level up your programming skills with 3,450 exercises across 52 languages, and insightful discussion with our volunteer team of welcoming mentors.
Exercism is
**100% free forever**.

## Community comments