C# - Check if string contains characters of another string at the same order

Question

I would like to check if a string contains the characters of another string (returning true or false), but it needs to be in the "right" order but not necessarily contiguous.

Example:

String firstWord = "arm";
String secondWord = "arandomword"; //TRUE - ARandoMword

String thirdWord = "road"; //FALSE - ARanDOmword

The word "arandomword" contains the letters of the word "road" but it's not possible to write it, because they are not at the right order.

Anyone, please?

Answer 1

Use regex. Something simple that passes your tests in linqpad:

void Main()
{
    String firstWord = "arm";
    String secondWord = "arandomword"; //TRUE - ARandoMword

    String thirdWord = "road";

    Regex.IsMatch(secondWord,makeRegex(firstWord.ToCharArray())).Dump();
}

// Define other methods and classes here
String makeRegex(char[] chars)
{
    StringBuilder sb = new StringBuilder();
    foreach (var element in chars.Select(c => Regex.Escape(c.ToString()))
        .Select(c => c + ".*"))
    {
        sb.Append(element);
    }
    return sb.ToString();
}

Answer 2

you could define an extension method like this:

public static class StringExtensions
{
    public static bool ContainsWord(this string word, string otherword)
    {
        int currentIndex = 0;

        foreach(var character in otherword)
        {
            if ((currentIndex = word.IndexOf(character, currentIndex)) == -1)
                return false;
        }

        return true;
    }
}

and call it as expressive as:

String firstWord = "arm";
String secondWord = "arandomword"; //TRUE - ARandoMword
String thirdWord = "road"; //FALSE - ARanDOmword

var ret = secondWord.ContainsWord(firstWord); // true
var ret2 = thirdWord.ContainsWord(firstWord); // false