CODEWITHSUNDEEP
c#stringfunctionsubstring
user3462831
user3462831

Reputation: 49

Is there any standard function to search for identical substrings within a string?

If I am having a string say for an example "ABEFAB", it would take a length parameter (eg. 2) and then return a result which would show that there ARE identical substrings of that length in my string.

Upvotes: 0

Views: 111

Answers (3)

Dmitrii Bychenko
Dmitrii Bychenko

Reputation: 186678

The simplest (however not that efficient) solution is

public static Boolean HasIdenticalSubStrings(String value, int length) 
{
  if (length <= 0)
    return false;
  else if (String.IsNullOrEmpty(value))
    return false;
  else if (value.Length <= length)
    return false;

  // HashSet is more efficient than List for Contains() operation
  HashSet<String> subStrings = new HashSet<String>();

  for (int i = 0; i <= value.Length - length; ++i) {
    String s = value.Substring(i, length);

    if (subStrings.Contains(s))
      return true;
    else
      subStrings.Add(s);
  }

  return false;
}

Test cases:

  HasIdenticalSubStrings("AAA", 2);    // true, overlaping "AA" substrings
  HasIdenticalSubStrings("ABxyAB", 2); // true
  HasIdenticalSubStrings("ABxAB", 2);  // true
  HasIdenticalSubStrings("ABCDEF", 2); // false

Upvotes: 1

Nikhil Agrawal
Nikhil Agrawal

Reputation: 48568

I think you are looking for this

public static bool HasIdenticalSubStrings(string str, int len)
{
    bool returnValue = false;

    List<String> lst = new List<string>();

    for (int i = 0; i <= str.Length - len; i++)
        lst.Add(str.Substring(i, len));

    returnValue = (lst.Distinct().Count() != lst.Count);

    return returnValue;
}

and call like

HasIdenticalSubStrings("ABEFAB", 2); //return true

HasIdenticalSubStrings("ABCDEF", 2); //return false

Note: You need to put some checks like String.IsNullOrEmpty check

Efficient Method:

public static bool HasIdenticalSubStrings(string str, int len)
{
    bool returnValue = false;

    List<String> lst = new List<string>();

    for (int i = 0; i <= str.Length - len; i++)
    {
        String tempstr = str.Substring(i, len);
        if (lst.Contains(tempstr))
        {
            returnValue = true;
            break;
        }
        else
            lst.Add(tempstr);
    }

    return returnValue;
}

Upvotes: 1

user3462831
user3462831

Reputation: 49

I think Contains surves this puprose quite well. It doesn't take any length parameters, though, but I discovered that for my program it's not even necessary because there is a determined block size which I use.

Upvotes: 0

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