寻找可能的组合

问题描述

我需要生成{"a", "b","c"}之间的所有可能组合.

I need to generate all possible combinations between {"a", "b","c"}.

例如，一个输入集，例如{"a", "b","c"}，预期输出是{"a", "b", "c" "ab", "ac", "bc", "abc"}.

For example, an input set say like {"a", "b","c"}, expected output is {"a", "b", "c" "ab", "ac", "bc", "abc"}.

推荐答案

听起来您正在寻找的基本上是电源设置.这是一个简单的实现(摘自本网站):

It sounds like what you're looking for is basically a form of power set. Here's a simple implementation (taken from this site):

public IEnumerable<IEnumerable<T>> GetPowerSet<T>(this IList<T> list)
{
    return from m in Enumerable.Range(0, 1 << list.Count)
           select
               from i in Enumerable.Range(0, list.Count)
               where (m & (1 << i)) != 0
               select list[i];
}

请注意，由于使用<<运算符，您将无法对包含30个以上元素的列表使用此方法.无论如何，我不建议您尝试使用一个包含那么多元素的列表，因为结果包含30个元素，结果集将包含2 或1073741824个元素.

Note that thanks to the << operator, you won't be able to use this method with lists that have more than 30 elements. I wouldn't recommend trying it with a list with close to that many elements anyway, since at 30 elements, the result set would contain 2 or 1073741824 elements.

您可以使用这种方法来获得所需的结果

You can use this method to get the result you want like this

public IEnumerable<string> GetPermutations(IList<string> strings)
{
    return from s in strings.GetPowerSet()
           select string.Concat(s);
}

但是，由于幂集包括空集，因此实际上将返回结果{"", "a", "b", "c", "ab", "ac", "bc", "abc"}.要过滤出空字符串，请使用以下命令:

However, because the power set includes the null set, this will actually return the result {"", "a", "b", "c", "ab", "ac", "bc", "abc"}. To filter out the empty string, use this:

public IEnumerable<string> GetPermutations(IList<string> strings)
{
    return from s in strings.GetPowerSet()
           let str = string.Concat(s)
           where str.Length > 0 // exclude null set result
           select str;
}

或更简单地说:

public IEnumerable<string> GetPermutations(IList<string> strings)
{
    return from s in strings.GetPowerSet().Skip(1)
           select string.Concat(s);
}

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