public void PermutationsShouldBeUnbiased(int count)
{
// Arrange
var data = Enumerable.Range(1, count).ToArray();
var permutations = PermutationLexicographicOrdering.EnumeratePermutations(data)
.ToDictionary(Stringify, x => 0);
var random = new RandomWithSeed();
var shuffle = new FisherYatesShuffle(random);
var idealNumberOfOccurrences = 10000;
var trials = permutations.Count * idealNumberOfOccurrences;
// Act
for (var i = 0; i < trials; ++i)
{
var tmp = Enumerable.Range(1, count).ToArray();
shuffle.Shuffle(tmp);
permutations[Stringify(tmp)]++;
}
// Assert
var deviation = 0.04;
var maxAllowed = (int)(idealNumberOfOccurrences * (1 + deviation));
var minAllowed = (int)(idealNumberOfOccurrences * (1 - deviation));
foreach (var pair in permutations)
{
var occurences = pair.Value;
var message = $"Expected permutation to be yielded {minAllowed} <= x <= {maxAllowed} times, " +
$"but was {occurences}. Seed: {random.Seed}";
Assert.True(occurences >= minAllowed && occurences <= maxAllowed, message);
}
}
public void ShouldNotModifyPermutationIfGivenOneIsLastAlready(int count)
{
// Arrange
var original = Enumerable.Range(1, count).OrderByDescending(x => x).ToArray();
var copy = new int[count];
Array.Copy(original, copy, count);
// Act
var wasFoundNext = PermutationLexicographicOrdering.NextPermutation(copy);
// Assert
Assert.False(wasFoundNext);
Assert.Equal(Stringify(original), Stringify(copy));
}
public void ShouldEnumeratePermutationsInLexicographicOrder(int count)
{
// Arrange
var expected = GetPermutations(Enumerable.Range(1, count).ToArray(), count)
.Select(Stringify)
.ToArray();
var input = Enumerable.Range(1, count).ToArray();
// Act
var actual = PermutationLexicographicOrdering.EnumeratePermutations(input)
.Select(Stringify)
.ToArray();
// Assert
Assert.True(actual.SequenceEqual(expected));
}
public void ShouldProperlyFindNextPermutationInLexicographicOrder(int count)
{
// Arrange
var permutations = GetPermutations(Enumerable.Range(1, count).ToArray(), count)
.ToArray();
for (var i = 0; i < permutations.Length - 1; ++i)
{
var input = permutations[i].ToArray();
var expected = permutations[i + 1];
// Act
var wasFoundNext = PermutationLexicographicOrdering.NextPermutation(input);
// Assert
Assert.True(wasFoundNext);
Assert.Equal(Stringify(expected), Stringify(input));
}
}
