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# jdehaan's solution

## to Pascal's Triangle in the C# Track

Published at Dec 21 2019 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution was written.

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
``````

## Running the tests

To run the tests, run the command `dotnet test` from within the exercise directory.

Initially, only the first test will be enabled. This is to encourage you to solve the exercise one step at a time. Once you get the first test passing, remove the `Skip` property from the next test and work on getting that test passing. Once none of the tests are skipped and they are all passing, you can submit your solution using `exercism submit PascalsTriangle.cs`

## Further information

For more detailed information about the C# track, including how to get help if you're having trouble, please visit the exercism.io C# language page.

## Source

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

### PascalsTriangleTest.cs

``````// This file was auto-generated based on version 1.5.0 of the canonical data.

using Xunit;

public class PascalsTriangleTest
{
[Fact]
public void Zero_rows()
{
Assert.Empty(PascalsTriangle.Calculate(0));
}

[Fact(Skip = "Remove to run test")]
public void Single_row()
{
var expected = new[]
{
new[] { 1 }
};
Assert.Equal(expected, PascalsTriangle.Calculate(1));
}

[Fact(Skip = "Remove to run test")]
public void Two_rows()
{
var expected = new[]
{
new[] { 1 },
new[] { 1, 1 }
};
Assert.Equal(expected, PascalsTriangle.Calculate(2));
}

[Fact(Skip = "Remove to run test")]
public void Three_rows()
{
var expected = new[]
{
new[] { 1 },
new[] { 1, 1 },
new[] { 1, 2, 1 }
};
Assert.Equal(expected, PascalsTriangle.Calculate(3));
}

[Fact(Skip = "Remove to run test")]
public void Four_rows()
{
var expected = new[]
{
new[] { 1 },
new[] { 1, 1 },
new[] { 1, 2, 1 },
new[] { 1, 3, 3, 1 }
};
Assert.Equal(expected, PascalsTriangle.Calculate(4));
}

[Fact(Skip = "Remove to run test")]
public void Five_rows()
{
var expected = new[]
{
new[] { 1 },
new[] { 1, 1 },
new[] { 1, 2, 1 },
new[] { 1, 3, 3, 1 },
new[] { 1, 4, 6, 4, 1 }
};
Assert.Equal(expected, PascalsTriangle.Calculate(5));
}

[Fact(Skip = "Remove to run test")]
public void Six_rows()
{
var expected = new[]
{
new[] { 1 },
new[] { 1, 1 },
new[] { 1, 2, 1 },
new[] { 1, 3, 3, 1 },
new[] { 1, 4, 6, 4, 1 },
new[] { 1, 5, 10, 10, 5, 1 }
};
Assert.Equal(expected, PascalsTriangle.Calculate(6));
}

[Fact(Skip = "Remove to run test")]
public void Ten_rows()
{
var expected = new[]
{
new[] { 1 },
new[] { 1, 1 },
new[] { 1, 2, 1 },
new[] { 1, 3, 3, 1 },
new[] { 1, 4, 6, 4, 1 },
new[] { 1, 5, 10, 10, 5, 1 },
new[] { 1, 6, 15, 20, 15, 6, 1 },
new[] { 1, 7, 21, 35, 35, 21, 7, 1 },
new[] { 1, 8, 28, 56, 70, 56, 28, 8, 1 },
new[] { 1, 9, 36, 84, 126, 126, 84, 36, 9, 1 }
};
Assert.Equal(expected, PascalsTriangle.Calculate(10));
}
}``````
``````ï»¿using System;
using System.Linq;
using System.Collections.Generic;

public static class PascalsTriangle
{
private static IEnumerable<int> CalculateRow(int row)
{
if (row == 1) {
yield return 1;
yield break;
}
var previousRow = CalculateRow(row - 1);
int previousValue = 0;
foreach (var currentValue in previousRow)
{
yield return currentValue + previousValue;
previousValue = currentValue;
}
yield return previousValue;
}

public static IEnumerable<IEnumerable<int>> Calculate(int rows)
{
return Enumerable
.Range(1, rows)
.Select(row => CalculateRow(row));
}
}``````