在c#中使用字符串数组生成组合
在c#中使用字符串数组生成组合
提问于 2012-12-04 08:50:12
string[] array = {"01", "02", "03", "04", "05", "06", "07", "08", "09", "10"};如何生成每个组合的2/3/4/5字符串，例如每个组合两个字符串，没有重复/重复，也不考虑位置，使用组合公式nCr =10/2！(10-2)！=45个组合。
我需要这样的输出：
"01", "02"
"01", "03"
"01", "04"
...
"02", "03" // eliminate the "02","01" 'cause it is same as "01","02" combination
"02", "04"
...然后生成3个字符串的组合，将有120个组合(根据nCr)。我需要这样的输出：
"01","02","03"
"01","02","04"
...而4个字符串的组合，将有210个组合，最少，每组合5个字符串的组合，将有252个组合。
我怎么写呢？我消耗了很多循环，看起来真的很混乱。
回答 3
Stack Overflow用户
回答已采纳
发布于 2012-12-04 09:25:48
您可以使用一个简单的递归：
private static IEnumerable<string> Combinations(int start, int level)
{
for ( int i = start; i < array.Length; i++ )
if ( level == 1 )
yield return array[i];
else
foreach ( string combination in Combinations(i + 1, level - 1) )
yield return String.Format("{0} {1}", array[i], combination);
}这样的称呼是：
var combinations = Combinations(0, 2);
foreach ( var item in combinations )
Console.WriteLine(item);Stack Overflow用户
发布于 2012-12-04 09:04:56
您可以使用这个高效的项目：Permutations, Combinations, and Variations using C# Generics。
string[] array = { "01", "02", "03", "04", "05", "06", "07", "08", "09", "10" };
int lowerIndex = 2;
var combinations = new Facet.Combinatorics.Combinations<String>(
array,
lowerIndex,
Facet.Combinatorics.GenerateOption.WithoutRepetition
);
foreach (IList<String> combis in combinations)
{
String combi = String.Join(" ", combis);
Console.WriteLine(combi);
}因为它是开源的，所以您可以查看它是如何实现的。但是上面的链接也是非常有用的。
输出(lowerIndex=2)：
01 02
01 03
01 04
01 05
01 06
01 07
01 08
01 09
01 10
02 03 <-- no 02 01 since it would be a repitition
02 04
02 05
// ... (45 combinations w/o repetitions)
09 10输出(lowerIndex=5)：
01 02 03 04 05
01 02 03 04 06
01 02 03 04 07
01 02 03 04 08
01 02 03 04 09
01 02 03 04 10
01 02 03 05 06
01 02 03 05 07
01 02 03 05 08
01 02 03 05 09
01 02 03 05 10
01 02 03 06 07
// ........... (252 combinations w/o repetitions)
05 07 08 09 10
06 07 08 09 10Stack Overflow用户
发布于 2012-12-04 09:05:21
下面是使用nCr对两个数字执行组合的函数，对多个数字进行调整
/// <summary>
/// Performs a nCr Combination of the two numbers
/// </summary>
/// <param name="n">The Number</param>
/// <param name="r">The Range</param>
/// <returns></returns>
public static double Combination(double n, double r)
{
/*
* Formula for Combination: n! / (r! * (n - r)!)
*/
// n and r should be integral values
double rfloor = Math.Floor(r);
double nfloor = Math.Floor(n);
// Check for all invalid values of n and r.
if ((n < 1) || (r < 0) || (r > n) || (r != rfloor) || (n != nfloor))
{
throw new Exception("Invalid Input to Combination Function: Number must be greater than Range");
}
return Factorial(n) / (Factorial(r) * Factorial(n - r));
}和
public static double Factorial(double n)
{
if (n < 0) { throw new Exception("Cannot take the factorial of a negative number"); }
double factorial = 1;
// 0! and 1! = 1
for (double i = 2; i < n + 1; i++)
{
factorial *= i;
}
return factorial;
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/13699043
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