how to extract common file path from list of file paths in c#

Question

What is the best way extract the common file path from the list of file path strings in c#?

Eg: I have a list 5 file paths in List variable, like below

c:\abc\pqr\tmp\sample\b.txt
c:\abc\pqr\tmp\new2\c1.txt
c:\abc\pqr\tmp\b2.txt
c:\abc\pqr\tmp\b3.txt
c:\abc\pqr\tmp\tmp2\b2.txt

output should be c:\abc\pqr\tmp

Answer 1

Because everything is best solved with LINQ*:
^{*not everything is best solved with LINQ.}

using System.Collections.Generic;
using System.IO;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        List<string> Files = new List<string>()
        {
            @"c:\abc\pqr\tmp\sample\b.txt",
            @"c:\abc\pqr\tmp\new2\c1.txt",
            @"c:\abc\pqr\tmp\b2.txt",
            @"c:\abc\pqr\tmp\b3.txt",
            @"c:\a.txt"
        };

        var MatchingChars =
            from len in Enumerable.Range(0, Files.Min(s => s.Length)).Reverse()
            let possibleMatch = Files.First().Substring(0, len)
            where Files.All(f => f.StartsWith(possibleMatch))
            select possibleMatch;

        var LongestDir = Path.GetDirectoryName(MatchingChars.First());
    }
}

---

Explanation:

The first line gets a list of lengths of possible matches to evaluate. We want the longest possibility first (so i reverse the enumeration which would be 0, 1, 2, 3; turning it into 3, 2, 1, 0).

I then get the string to match, which is simply a substring of the first entry of the given length.

I then filter the results, to ensure we only include possible matches that all files start with.

Finally, i return the first result, which will be the longest substring and call path.getdirectoryname to ensure if something has a few identical letters in the filenames it isn't included.

Answer 2

I don't think there's a "trick"to get past using the brute force method to do this comparison, but you can optimize your solution somewhat:

Prepare:
Find the shortest string

Repeat:
See if all of the other strings contain it
If so, you're done
If not, remove one or more characters