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

Answer 3

Something like this?

bool HasLettersInOrder(string firstWord, string secondWord)
{
    int lastPos = -1;
    foreach (char c in firstWord)
    {
        lastPos++;
        while (lastPos < secondWord.Length && secondWord[lastPos] != c)
            lastPos++;
        if (lastPos == secondWord.Length)
            return false;
    }
    return true;
}

Answer 4

I can not check right now, but something along the lines:

int i = 0, j = 0;

while(i < first.Length && j < second.Length)
{
   while(first[i] != second[j] && j < second.Length) j++;
   i++;
   j++
}

bool b = i == first.Length;

Answer 5

Thanks for all the replies. I've tried and tried and I did it my way. Definitively it's not the shortest way to do it, but at least it's working:

    public static Boolean checkWords(String smallerWord, String biggerWord)
    {
        int position = 0;
        bool gotFirst = false;
        bool gotAnother = false;
        int positionBigger = 0;
        String word = "";

        for(int positionSmaller = 0; positionSmaller < smallerWord.Length; positionSmaller++)
        {
            if(!gotFirst)
            {
                if(biggerWord.Contains(smallerWord[positionSmaller].ToString()))
                {
                    position = biggerWord.IndexOf(smallerWord[positionSmaller].ToString());
                    gotFirst = true;
                    word = smallerWord[positionSmaller].ToString();
                }
            }
            else
            {
                gotAnother = false;
                positionBigger = position + 1;

                while(!gotAnother)
                {
                    if(positionBigger < biggerWord.Length)
                    {
                        if(biggerWord[positionBigger].ToString().Equals(smallerWord[positionSmaller].ToString()))
                        {
                            position = positionBigger;
                            gotAnother = true;
                            word += smallerWord[positionSmaller].ToString();
                        }
                        else
                        {
                            positionBigger++;
                        }
                    }
                    else
                    {
                        gotAnother = true;
                    }
                }
            }
        }

        if(smallerWord.Equals(word))
        {
            return true;
        }
        else
        {
            return false;
        }
    }