You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
TrustPilotChallenge/dotnet/WhiteRabbit/PrecomputedPermutationsGene...

112 lines
3.4 KiB

8 years ago
namespace WhiteRabbit
{
using System;
8 years ago
using System.Collections.Generic;
using System.Linq;
internal static class PrecomputedPermutationsGenerator
8 years ago
{
private static ulong[][][] Permutations { get; } = Enumerable.Range(0, 9).Select(GeneratePermutations).ToArray();
private static long[] PermutationsNumbers { get; } = GeneratePermutationsNumbers().Take(19).ToArray();
public static ulong[] HamiltonianPermutations(int n, uint filter) => Permutations[n][filter];
public static long GetPermutationsNumber(int n) => PermutationsNumbers[n];
private static ulong[][] GeneratePermutations(int n)
{
if (n == 0)
{
return new ulong[0][];
}
var allPermutations = PermutationsGenerator.HamiltonianPermutations(n)
.Select(FormatPermutation)
.ToArray();
var statesCount = (uint)1 << (n - 1);
var result = new ulong[statesCount][];
for (uint i = 0; i < statesCount; i++)
{
result[i] = PadToWholeChunks(FilterPermutations(allPermutations, i).ToArray(), Constants.PhrasesPerSet);
}
return result;
}
private static IEnumerable<ulong> FilterPermutations(IEnumerable<ulong> permutations, uint state)
{
for (int position = 0; position < 16; position++)
{
if (((state >> position) & 1) != 0)
{
var innerPosition = (uint)position;
permutations = permutations.Where(permutation => IsOrderPreserved(permutation, innerPosition));
}
}
return permutations;
}
public static bool IsOrderPreserved(ulong permutation, uint position)
{
var currentPermutation = permutation;
while (currentPermutation != 0)
{
if ((currentPermutation & 15) == position)
{
return true;
}
if ((currentPermutation & 15) == (position + 1))
{
return false;
}
currentPermutation = currentPermutation >> 4;
}
throw new ApplicationException("Malformed permutation " + permutation + " for position " + position);
}
private static T[] PadToWholeChunks<T>(T[] original, int chunkSize)
{
if (original.Length % chunkSize == 0)
{
return original;
}
return original.Concat(Enumerable.Repeat(default(T), chunkSize - (original.Length % chunkSize))).ToArray();
}
private static ulong FormatPermutation(PermutationsGenerator.Permutation permutation)
{
System.Diagnostics.Debug.Assert(permutation.PermutationData.Length <= 16);
ulong result = 0;
for (var i = 0; i < permutation.PermutationData.Length; i++)
8 years ago
{
result |= (ulong)(permutation.PermutationData[i]) << (4 * i);
8 years ago
}
8 years ago
return result;
8 years ago
}
private static IEnumerable<long> GeneratePermutationsNumbers()
{
long result = 1;
yield return result;
var i = 1;
while (true)
{
result *= i;
yield return result;
i++;
}
}
8 years ago
}
}