LINQで7クイーン(書類選考無し＆高級うなぎGET)

問題はこちら。
実行結果はこちら。

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;

struct Queen
{
  public int X;
  public int Y;
  public Queen(int x, int y)
  {
    this.X = x;
    this.Y = y;
  }
  public bool IsMovable(Queen q)
  {
    return (this.X == q.X) || (this.Y == q.Y) || this.IsDiagonal(q);
  }
  public bool IsDiagonal(Queen q)
  {
    var diffX = this.X - q.X;
    var diffY = this.Y - q.Y;
    return (diffX == diffY || diffX == -diffY);
  }
}

class Program
{
  static void Main()
  {
    var letters = new string[]
    {
      "lhikoav",
      "rqsczlp",
      "uwalnfo",
      "tykajeh",
      "ahitsyd",
      "efoptxn",
      "ruzwyve"
    };
    var result =
      from q1 in Enumerable.Range(1, 7).Select(x => new Queen(x, 1))
      from q2 in Enumerable.Range(1, 7).Select(x => new Queen(x, 2))
      from q3 in new Queen[] {new Queen(3, 3)}
      from q4 in Enumerable.Range(1, 7).Select(x => new Queen(x, 4))
      from q5 in new Queen[] {new Queen(4, 5)}
      from q6 in Enumerable.Range(1, 7).Select(x => new Queen(x, 6))
      from q7 in Enumerable.Range(1, 7).Select(x => new Queen(x, 7))
      let queens = new Queen[] {q1, q2, q3, q4, q5, q6, q7}
      where Combinations(queens).All(t => !t[0].IsMovable(t[1]))
      select new string((from q in queens
                         orderby q.X * q.Y
                         select letters[q.Y - 1][q.X - 1])
                        .ToArray());
    foreach (var s in result)
      Console.WriteLine(s);
  }

  static IEnumerable<T[]> Combinations<T>(IEnumerable<T> source)
  {
    var list = new List<T>(source);
    for (var i = 0; i < list.Count; i++)
      for (var j = i + 1; j < list.Count; j++)
        yield return new T[] {list[i], list[j]};
  }
}