check whether part of one string in another string

If I understand your requirement correctly, you have to split string1 into separate words. String.Split()[^] can help you here.

Then, you have to concatenate every word with its successor to get several sequences of two subsequent words from string2. In this case, I would choose a simple + in favor of a StringBuilder[^].

Then you can use String.Contains()[^] with all those two-word-sequences to get their occurences within string2.

You can try the following solution

void Main()
{

//This routine tests whether str2 or part of it is present in str1
//eg. first, first test, first test for etc.
string str1 = "This is first test string";
string str2 = "first test   for me";
string stringToFind=str2;
int spaceIndex;
    while (true){
        //Check whether str1 contains stringToFind
        if (str1.Contains(stringToFind)){
            Console.WriteLine("Str1 contains: " + stringToFind);
            break;
        }
        //Find the last position of space
        spaceIndex=stringToFind.LastIndexOf(' ');
        //If no space is left in the stringToFind, then we have searched
        //the first word already.  Hence, no more words to search. So quick loop
        if(spaceIndex==-1)
            break;
        //Trim is required to remove the trailing spaces, as the last index of
        //finds the last space.
        stringToFind = stringToFind.Substring(0,spaceIndex).Trim();
    }
}

If your problem is solved you may accept the solution, otherwise please post your queries.

PES

Try Googling "Longest common subsequence" ;)

Maybe this could help...

public static Boolean isContainingParts(String Container_, String Parts_) {
    Boolean found = false;
    
    String[] parts = Parts_.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
    IEnumerator enumerator = parts.GetEnumerator();
    
    while(!found && enumerator.MoveNext()) {
        found = Container_.Contains(enumerator.Current.ToString());
    }
    
    return found;
    
}

[edit]ooops... should've pressed refresh before posting :)[/edit]