Published at Oct 02 2019
·
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
```

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`

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.

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

```
// 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));
}
}
```

```
using System;
using System.Collections.Generic;
public static class PascalsTriangle
{
public static IEnumerable<IEnumerable<int>> Calculate(int rows)
{
if (rows>0)
{
for (int i = 1; i <= rows; i++)
{
yield return PascalsTriangleRow(i);
}
}
}
public static int Factorial(int n)
{
int res = 1;
while (n >= 1)
{
res *= n;
n--;
}
return res;
}
public static int BinomCoef(int n, int r)
{
if (n >= r)
{
return Factorial(n) / (Factorial(n - r) * Factorial(r));
}
return 0;
}
public static IEnumerable<int> PascalsTriangleRow(int row)
{
if (row > 0)
{
for (int i = 0; i < row; i++)
{
yield return BinomCoef(row-1, i);
}
}
}
}
```

A huge amount can be learned from reading other people’s 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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