how to extract common file path from list of file paths in c#
using System.Collections.Generic;
using System.IO;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        List<string> Files = new List<string>()
        {
            @"c:abcpqrtmpsampleb.txt",
            @"c:abcpqrtmpnew2c1.txt",
            @"c:abcpqrtmpb2.txt",
            @"c:abcpqrtmpb3.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());
    }
}

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

string commonPath(string[] paths) {
    // this is a Java notation, I hope it's right in C# as well? Let me know!
    string[][] tokens = new string[paths.length][];

    for(int i = 0; i < paths.Length; i++) {
        tokens[i] = paths.Split('\');
    }

    string path = "";

    for(int i = 0; i < tokens[0].Length; i++) {
        string current = tokens[0][i];
        for(int j = 1; j < tokens.Length; j++) {
            if(j >= tokens[i].Length) return path;
            if(current != tokens[i][j]) return path;
        }
        path = path + current + '\';
    }
    return path; // shouldn't reach here, but possible on corner cases
}

List<string> list1 = new List<string>();
list1.Add(@"c:abcpqrtmpsampleb.txt");
list1.Add(@"c:abcpqrtmpnew2c1.txt");
list1.Add(@"c:abcpqrtmpb2.txt");
list1.Add(@"c:abcpqrtmpb3.txt");
list1.Add(@"c:abcpqrtmptmp2b2.txt");

string baseDir = "";
foreach (var item in list1)
{
    if (baseDir == "")
        baseDir = System.IO.Path.GetDirectoryName(item);
    else
    {
        int index = 0;
        string nextDir = System.IO.Path.GetDirectoryName(item);
        while (index< baseDir.Length && index<nextDir.Length &&
            baseDir[index] == nextDir[index])
        {
            index++;
        }
        baseDir = baseDir.Substring(0, index);
    }
}
MessageBox.Show(baseDir);

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

namespace stackoverflow1
{
    class MainClass
    {
        public static void Main (string[] args)
        {
            List<String> paths=new List<String>();
            paths.Add(@"c:abcpqrtmpsampleb.txt");
            paths.Add(@"c:abcpqrtmpnew2c1.txt");
            paths.Add(@"c:abcpqrtmpb2.txt");
            paths.Add(@"c:abcpqrtmpb3.txt");
            paths.Add(@"c:abcpqrtmptmp2b2.txt");

            Console.WriteLine("Found: "+ShortestCommonPath(paths));

        }

        private static String ShortestCommonPath(IList<String> list)
        {
            switch (list.Count)
            {
            case 0: return null;
            case 1: return list[0];
            default:
                String s=list[0];
                while (s.Length>0)
                {
                    bool ok=true;
                    for (int i=1;i<list.Count;i++)
                    {
                        if (!list[i].StartsWith(s))
                        {
                            ok=false;
                            int p=s.LastIndexOf(Path.DirectorySeparatorChar);
                            if (p<0) return "";
                            s=s.Substring(0,p);
                            break;
                        }
                    }
                    if (ok) break;
                }
                return s;
            }
        }

    }
}

void Main()
{
    string[] paths = new[] { @"c:abcpqrtmpsampleb.txt",
                            @"c:abcpqrtmpnew2c1.txt",
                            @"c:abcpqrtmpb2.txt",
                            @"c:abcpqrtmpb3.txt",
                            @"c:abcpqrtmptmp2b2.txt"};

    var test = new List<string>();
    var common = paths[0].Split('\').TakeWhile ( segment =>
    {
        test.Add ( segment );
        return paths.All ( path => path.StartsWith ( String.Join ("\", test )  + "\") ) ;
    } );

    Console.WriteLine ( String.Join ("\", common ) );
}