Notice the difference between the below two approaches, loops are faster than recursion. it means the cost of calling recursive function cannot be ignored, so try to use loops instead of recursion.
below program computes the combination of string, using loops and recursion.
static void Main(string[] args)
{
string str = "abcd";
ArrayList hash = new ArrayList();
DateTime start = DateTime.Now;
combination(str, str.Length, hash);
Console.WriteLine(DateTime.Now - start);
char[] output = new char[27];
for (int h = 0; h < 27; h++)
output[h] = new char();
start = DateTime.Now;
combination_book(str, output, str.Length, 0, 0);
Console.WriteLine(DateTime.Now - start);
Console.ReadLine();
}
private static void combination_book(string s,char[] output, int len, int recLen, int start)
{
for (int i = start; i < len; i++)
{
output[recLen] = s[i];
output[recLen + 1] = '';
Console.WriteLine(output);
if (i < len - 1)
combination_book(s, output, len, recLen + 1, i + 1);
}
}
private static void combination(string s, int len, ArrayList hash)
{
hash.Add(s[len - 1].ToString());
Console.WriteLine(s[len - 1].ToString());
for (int i = len - 2; i >= 0; i--)
{
ArrayList tempHash = new ArrayList();
tempHash.Add(s[i].ToString());
Console.WriteLine(s[i].ToString());
foreach (string comb in hash)
{
tempHash.Add(s[i].ToString() + comb);
Console.WriteLine(s[i].ToString() + comb);
}
hash.AddRange(tempHash);
}
}
And the output
d c cd b bd bc bcd a ad ac acd ab abd abc abcd 00:00:00 a ab abc abcd abd ac acd ad b bc bcd bd c cd d 00:00:00.0156249
but when the string become long then you might have to use recursion.
