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using System;
using System.Collections.Generic;
using System.Linq;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
int cnt = 0;
foreach (var q in NQueens(8))
{
Console.Write($"第{++cnt,2}个排列:");
q.ForEach(x => Console.Write($" {x}"));
Console.WriteLine();
}
}
public static IEnumerable<List<int>> NQueens(int n)
{
foreach (var r in NQueens(n, n))
yield return r;
}
static IEnumerable<List<int>> NQueens(int n, int row)
{
if (row == 1)
for (var i = 1; i <= n; i++)
yield return new List<int> { i };
else
{
foreach (var r in NQueens(n, row - 1))
{
for (var i = 1; i <= n; i++)
if (检测不攻击(row, i, r))
{
var clone = r.ToList();
clone.Add(i);
yield return clone;
}
}
yield break;
}
bool 检测不攻击(int row, int column, List<int> queens)
{
for (var i = 1; i <= queens.Count; i++)
if (检测攻击(row, column, i, queens[i - 1]))
return false;
return true;
}
bool 检测攻击(int r1, int c1, int r2, int c2)
{
return c1 == c2 || Math.Abs(r1 - r2) == Math.Abs(c1 - c2);
}
}
}
}
这里就使用了“迭代器技术”来回溯各种可行解。 foreach (var q in NQueens(8).Take(3))
foreach (var q in NQueens(8).Where(r => r[7]==3 || r[7]==4).Take(3))