DouKaku?

using System;
using System.Collections.Generic;
using System.IO;
static class Program {
    public static void Main(String[] args) {
        // 行ごとに読み込んで
        List<string> words = new List<string>();
        using(StreamReader sr = new StreamReader(args[0])) {
            foreach(string line in sr.ReadToEnd().Split('\n', '\r')) {
                if (line != string.Empty && !words.Contains(line)) {
                    words.Add(line);
                }
            }
            words.Sort();
        }
        // 重複文字数をチェックして
        List<int> indexes = new List<int>(); {
            int[] itemp = new int[words.Count];
            for(int i = words.Count - 1; 1 <= i; i--) {
                int to = Math.Min(words[i - 1].Length, words[i].Length);
                for(int j = 0; j < to && words[i - 1][j] == words[i][j]; j++) {
                    itemp[i]++;
                }
            }
            indexes.AddRange(itemp);
        }
        // 重複文字数を多い順に並び替えて
        List<int> times = new List<int>(); {
            foreach(int cnt in indexes) {
                if (!times.Contains(cnt))
                    times.Add(cnt);
            }
            times.Sort();
            times.Reverse();
        }
        // 重複部分を削っていく
        foreach(int steps in times) {
            for(int i = words.Count - 1; 0 < i; i--) {
                if (indexes[i] == steps) {
                    words[i - 1] = string.Format("{0}(?:{1}|{2})",
                        words[i - 1].Substring(0, steps),
                        words[i - 1].Substring(steps),
                        words[i].Substring(steps));
                    words.RemoveAt(i);
                    indexes.RemoveAt(i);
                }
            }
        }
        string result = "^" + words[0] + "$";
        Console.WriteLine(result);
    }
}