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B1tF8er's solution

to Pascal's Triangle in the C# Track

Published at Sep 21 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

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));
    }
}
using System;
using System.Collections.Generic;

public static class PascalsTriangle
{
    public static IEnumerable<IEnumerable<int>> Calculate(int rows)
    {
        for (var i = 1; i <= rows; i++)
            yield return Row(i);
    }

    private static IEnumerable<int> Row(int row)
    {
        yield return 1;
        var column = 1;

        for (var j = 1; j < row; j++)
        {
            column = column * (row - j) / j;
            yield return column;
        }
    }

}

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