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.