Exclude Similarities in List of Strings to extract the Difference

Question

I have a list of sentences that are the same except for the Title of the book.

How can I loop through the list and exclude the similarities to find the title of the book

Answer 1

This was an interesting problem, so I've played around with it a little and came up with the following (cumbersome) solution:

Find the first index where any of the sentences have a different char, then do the same in the reversed sentences, and then use Substring to extract only the different parts of the sentences:

List<string> ExtractDifferences(List<string> sentences)
{
    var firstDiffIndex = GetFirstDifferenceIndex(sentences);
    var lastDiffIndex = GetFirstDifferenceIndex(sentences.Select(s => new string(s.Reverse().ToArray())).ToList());
    return sentences.Select(s => s.Substring(firstDiffIndex, s.Length - lastDiffIndex - firstDiffIndex)).ToList();
}


int GetFirstDifferenceIndex(IList<string> strings)
{
    int firstDifferenceIndex = int.MaxValue;

    for (int i = 0; i < strings.Count; i++)
    {
        var current = strings[i];
        var prev = strings[i == 0 ? strings.Count - 1 : i - 1];

        var firstDiffIndex = current
            .Select((c, j) => new { CurrentChar = c, Index = j })
            .FirstOrDefault(ci => ci.CurrentChar != prev[ci.Index])
            .Index;

        if (firstDiffIndex < firstDifferenceIndex)
        {
            firstDifferenceIndex = firstDiffIndex;
        }
    }
    return firstDifferenceIndex;
}

I guess the GetFirstDifferenceIndex method can be written differently, perhaps better using linq, but I don't have enough time to play with it.

You can see a live demo on rextester.

Answer 2

A working solution using LINQ:

List<string> sentences = new List<string>() { };
List<string> titles = new List<string>() { };

sentences.Add("The book named Lord of the Flies is a classic.");
sentences.Add("The book named To Kill a Mockingbird is a classic.");
sentences.Add("The book named The Catcher in the Rye is a classic.");
sentences.Add("Hello");
sentences.Add("The book named ");


titles = sentences.Where(sentence => sentence.Length > "The book named ".Length + " is a classic".Length)
            .GroupBy(sentence => sentence.Substring(0, 15), sentence => sentence.Remove(sentence.Length - " is a classic".Length).Substring("The book named ".Length))
            .Where(g => g.Key == "The book named ")
            .SelectMany(g => g)
            .ToList();

foreach (var title in titles)
    WriteLine(title);

First, it filters out sentences too short to meet the criteria, then groups the results by first 15 letters and extracts the titles with String.Remove.