[英]C# recursive loop
我有这些数据
string [] letters = {"a","b","c"};
我想要一个类似generateString(1)的函数,如果value为1,则输出为:
a
b
c
如果generateString(3),则输出为
a
b
c
aa
ab
ac
ba
bb
bc
ca
cb
cc
aaa
aab
aac
aba
abb
abc
aca and so on...
我可以这样
foreach(var a in data){
foreach(var b in data){
foreach(var c in data){
Console.WriteLine(a + b + c);
}
}
}
它最多只能生成3,如果我想使其达到4,则我要添加另一个foreach,这是我认为不是一个更好的主意。
有什么建议么?
看起来像这样
List<List<String>> foo(int i){
if(i==1){
return new List<List<String>>(new List<String>("a", "b", "c"));
} else{
var result = new List<List<String>>();
foreach(List<String> list in foo(i-1)){
foreach(String elem in new String[]{"a", "b", "c"}){
var tmp = new List<String>(list);
tmp.Add(elem);
result.Add(tmp);
}
}
return result;
}
}
我不确定sintax和list构造函数,但总的来说是这样
static string[] generateString(string[] letters, int len)
{
if (len < 0) throw new ArgumentOutOfRangeException("length can't be less than zero.");
switch (len)
{
case 0: return new string[0];
case 1: return letters;
default:
// all possible combinations which are shorter than required
// recursion is used here
var shorter_x = generateString(letters, len - 1).ToArray();
// all combinations which have length = len - 1
var shorter_1 = shorter_x.Where(line => line.Length == len - 1).ToArray();
// resulting array
return shorter_x.Union(letters.SelectMany(letter => shorter_1.Select(shorter => letter + shorter))).ToArray();
}
}
UPD:将数据表示为
char[] letters = { 'a', 'b', 'c' }
会更加一致。 在这种情况下,该功能看起来像
static string[] generateString(char[] letters, int len)
{
if (len < 0) throw new ArgumentOutOfRangeException("length can't be less than zero.");
switch (len)
{
case 0: return new string[0];
case 1: return letters.Select(char.ToString).ToArray();
default:
......
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