String array: search for text, return line number of first occurrence

Question

In my string array, I want to look up some text and return the the line number of the first occurrence as an int.

This is working;

public static int LookUpLineNumber(String[] item, string TextToLookUp)
{
    int m;
    for (m = 0; m < item.Count(); m++)
    {
        if (item[m].Contains(TextToLookUp))
        {
            break;
        }
    }
    return m++;
}

However, I am wondering if there is any way to optimize it for efficiency and length?

Speed comparison: (average time on 10.000 runs with an string array of size 10.000)

1. Using my code:

   • 1,259ms

2. Using Habib's code: Array.FindIndex<string>(item, r => r.Contains(TextToLookUp));

   • 0,906ms

Answer 1

Your current solution looks OK. You can have return m; instead of return m++ .

If you want to shorten your code you can use Array.FindIndex<T> like:

public static int LookUpLineNumber(String[] item, string TextToLookUp)
{
    return Array.FindIndex<string>(item, r => r.Contains(TextToLookUp));
}

Not really sure if it would give you any performance gain.

Answer 2

If you need to do this multiple times, a suffix tree built out of the array would be the fastest approach:

http://en.wikipedia.org/wiki/Suffix_tree

However, if you are not re-using the array, then I think the approach you have is likely fastest, short of using a regex to do the contains, which may be faster if the regex is pre-compiled.

Answer 3

You can also do the following :-

Array.FindIndex(item,i=>i.Contains(TextToLookUp));

The above would work even if it is not sorted.

The above can be further optimized by using IndexOf operations instead of Contains and passing StringComparison.OrdinalIgnoreCase . Then you will have to compare it against 0.