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

Published at Aug 28 2020
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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 './pascals-triangle'
describe 'Pascal', ->
it 'one row', ->
pascal = new PascalsTriangle()
expect(pascal.rows(0)).toEqual []
xit 'two rows', ->
pascal = new PascalsTriangle()
expect(pascal.rows(1)).toEqual [[1]]
xit 'three rows', ->
pascal = new PascalsTriangle()
expect(pascal.rows(2)).toEqual [[1], [1,1]]
xit 'four rows', ->
pascal = new PascalsTriangle()
expect(pascal.rows(3)).toEqual [[1], [1,1], [1,2,1]]
xit 'five rows', ->
pascal = new PascalsTriangle()
expect(pascal.rows(4)).toEqual [[1], [1,1], [1,2,1], [1,3,3,1]]
xit 'five rows', ->
pascal = new PascalsTriangle()
expect(pascal.rows(5)).toEqual [[1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1]]
xit 'six rows', ->
pascal = new PascalsTriangle()
expect(pascal.rows(6)).toEqual [[1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1], [1, 5, 10, 10, 5, 1]]
xit 'ten rows', ->
pascal = new PascalsTriangle()
expect(pascal.rows(10)).toEqual [[1], [1, 1], [1, 2, 1], [1, 3, 3, 1], [1, 4, 6, 4, 1], [1, 5, 10, 10, 5, 1], [1, 6, 15, 20, 15, 6, 1], [1, 7, 21, 35, 35, 21, 7, 1], [1, 8, 28, 56, 70, 56, 28, 8, 1], [1, 9, 36, 84, 126, 126, 84, 36, 9, 1]]
```

```
class PascalsTriangle
constructor: ->
return
rows: (len) ->
return [] if (len is 0)
return [[ 1 ]] if (len is 1)
result = []
renderRow = (row) ->
renderCol = (col) ->
return 1 if (col is 0) or (col is row-1)
r = result[ row-2 ]
return r[ col-1 ] + r[ col ]
result.push [ 0...row ].map(renderCol)
return
[ 1..len ].map renderRow
return result
module.exports = PascalsTriangle
```

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?

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