List of integer ranges in C#

Question

I have a few classes that have a sequence of integer, those sequences are registered in another class that checks if a number in the sequence isn't already used.

The sequences are for the most contiguous, going from a number to another.

For now I've been using a simple List that means if a sequence represents from 5000 to 15000 there will be 10000 elements in the List. I would like to replace it by something more suitable that can represents range in a simple element.

In my particular case, I would also like those ranges to represent an object (the class where the sequence originated from), so that when I lookup for a number, I have access to its origin rather than looking through each class to see if they contain the number I'm looking for.

Here is my pseudocode with the results I expect:

/* int is the integer type, while string is the "tag" object */
var animals = new IntRangeArray<int, string>();

animals.Add(1, "dog");
// [0] begin: 1, end: 1, object: "dog"

animals.Add(2, "dog");
// [0] begin: 1, end: 2, object: "dog"

/* AddRange with C#7.0 ValueTuple */
animals.AddRange((4,14), "dog");
// [0] begin: 1, end: 2, object: "dog"
// [1] begin: 4, end: 14, object: "dog"

animals.Add(3, "dog");
// [0] begin: 1, end: 14, object: "dog" 
/* All sequences have been merged because they are contiguous and have the same tag */

animals.AddRange( new int[]{ 15, 17, 18, 19 }, "dog");
// [0] begin: 1, end: 15, object: "dog"
// [1] begin: 17, end: 19, object: "dog"

animals.Add(16, "cat"); 
// [0] begin: 1, end: 15, object: "dog"
// [1] begin: 16, end: 16, object: "cat"
// [2] begin: 17, end: 19, object: "dog"

animals.Remove(8);
// [0] begin: 1, end: 7, object: "dog"
// [1] begin: 9, end: 15, object: "dog"
// [2] begin: 16, end: 16, object: "cat"
// [3] begin: 17, end: 18, object: "dog"

animals.At(11);
// struct { Begin = 9, End = 15, Tag = "dog" }

animals.RemoveWithTag("dog");
// [0] begin: 16, end: 16, object: "cat"

animals.TagOf(16);
// "cat"

I could not find any classes within the .NET Framework that implements this behavior so I would like to know how could I implement this or if there is any already existing implementation.

Answer 1

For this kind of thing I usually end up writing my own classes. Here's what I would do for this:

First, the Range class, which has a Begin, End, and Tag. It also has some helper methods to simplify querying for ranges that are overlapping and adjacent, or for doing case-insensitive tag comparison, and for outputting a string value:

class Range
{
    public int Begin { get; set; }
    public int End { get; set; }
    public string Tag { get; set; }

    public bool CombineWith(Range other)
    {
        Range combinedRange;
        if (TryCombine(this, other, out combinedRange))
        {
            this.Begin = combinedRange.Begin;
            this.End = combinedRange.End;
            return true;
        }

        return false;
    }

    public bool IsAdjacentTo(Range other)
    {
        return AreAdjacent(this, other);
    }

    public bool OverlapsWith(Range other)
    {
        return AreOverlapping(this, other);
    }

    public bool ContainsIndex(int index)
    {
        return this.Begin <= index && this.End >= index;
    }

    public bool TagEquals(string tag)
    {
        if (this.Tag == null) return tag == null;
        return this.Tag.Equals(tag, StringComparison.OrdinalIgnoreCase);
    }

    public static bool TryCombine(Range first, Range second, out Range combined)
    {
        combined = new Range();

        if (first == null || second == null) return false;
        if (!TagsEqual(first, second)) return false;
        if (!AreAdjacent(first, second) && !AreOverlapping(first, second)) return false;

        combined.Begin = Math.Min(first.Begin, second.Begin);
        combined.End = Math.Max(first.End, second.End);
        combined.Tag = first.Tag;

        return true;
    }

    public static bool AreAdjacent(Range first, Range second)
    {
        if (first == null || second == null) return false;
        if (!Range.TagsEqual(first, second)) return false;

        return (first.Begin == second.End + 1) ||
               (first.End == second.Begin - 1);
    }

    public static bool AreOverlapping(Range first, Range second)
    {
        if (first == null || second == null) return false;

        return (first.Begin >= second.Begin && first.Begin <= second.End) ||
               (first.End >= second.Begin && first.End <= second.End);
    }

    public static bool TagsEqual(Range first, Range second)
    {
        if (first == null || second == null) return false;
        return first.TagEquals(second.Tag);
    }

    public override string ToString()
    {
        return $"begin: {Begin}, end: {End}, tag: {Tag}";
    }
}

Next is your IntRangeArray class, which manages the adding and removing of items in the a list of Range objects:

class IntRangeArray
{
    private readonly List<Range> ranges = new List<Range>();

    public bool Add(int index, string tag)
    {
        return AddRange(index, index, tag);
    }

    public bool AddRange(IEnumerable<int> indexes, string tag)
    {
        if (indexes == null || string.IsNullOrWhiteSpace(tag)) return false;

        bool result = true;

        foreach (var index in indexes)
        {
            if (!Add(index, tag)) result = false;
        }

        return result;
    }

    public bool AddRange(Tuple<int, int> range, string tag)
    {
        return AddRange(range.Item1, range.Item2, tag);
    }

    public bool AddRange(int begin, int end, string tag)
    {
        if (begin < 0 || end < 0 || string.IsNullOrWhiteSpace(tag)) return false;

        var newRange = new Range {Begin = begin, End = end, Tag = tag};
        var overlappingRanges = ranges.Where(r => r.OverlapsWith(newRange)).ToList();
        var adjacentRanges = ranges.Where(r => r.IsAdjacentTo(newRange)).ToList();

        if (overlappingRanges.Any())
        {
            if (!overlappingRanges.All(r => r.TagEquals(newRange.Tag)))
            {
                return false;
            }

            foreach (var overlappingRange in overlappingRanges)
            {
                newRange.CombineWith(overlappingRange);
                ranges.Remove(overlappingRange);
            }
        }

        foreach (var adjacentRange in adjacentRanges)
        {
            newRange.CombineWith(adjacentRange);
            ranges.Remove(adjacentRange);
        }

        ranges.Add(newRange);
        return true;
    }

    public string At(int index)
    {
        var matchingRange = ranges.SingleOrDefault(r => r.ContainsIndex(index));
        return matchingRange?.ToString() ?? $"No item exists at {index}";
    }

    public void Remove(int index)
    {
        var matchingRange = ranges.SingleOrDefault(r => r.ContainsIndex(index));
        if (matchingRange == null) return;

        if (matchingRange.Begin == matchingRange.End)
        {
            ranges.Remove(matchingRange);
        }
        else if (index == matchingRange.Begin)
        {
            matchingRange.Begin += 1;
        }
        else if (index == matchingRange.End)
        {
            matchingRange.End -= 1;
        }
        else
        {
            // Split the range by creating a new one for the beginning
            var newRange = new Range
            {
                Begin = matchingRange.Begin,
                End = index - 1,
                Tag = matchingRange.Tag
            };

            matchingRange.Begin = index + 1;
            ranges.Add(newRange);
        }            
    }

    public void RemoveWithTag(string tag)
    {
        ranges.RemoveAll(r => r.TagEquals(tag));
    }

    public string TagOf(int index)
    {
        var matchingRange = ranges.SingleOrDefault(r => r.ContainsIndex(index));
        return matchingRange == null ? $"No item exists at {index}" : matchingRange.Tag;
    }

    public override string ToString()
    {
        if (ranges == null || !ranges.Any()) return "No items exist.";

        ranges.Sort((x, y) => x.Begin.CompareTo(y.Begin));
        var output = new StringBuilder();

        for(int i = 0; i < ranges.Count; i++)
        {
             output.AppendLine($"[{i}] {ranges[i]}");
        }

        return output.ToString();
    }
}

To test it out, I just copied and pasted your code sample above:

private static void Main()
{
    /* int is the integer type, while string is the "tag" object */
    var animals = new IntRangeArray();

    animals.Add(1, "dog");
    Console.WriteLine(animals);

    animals.Add(2, "dog");
    Console.WriteLine(animals);

    /* AddRange with C#7.0 ValueTuple */
    animals.AddRange(Tuple.Create(4, 14), "dog");
    Console.WriteLine(animals);

    animals.Add(3, "dog");
    Console.WriteLine(animals);

    animals.AddRange(new int[] { 15, 17, 18, 19 }, "dog");
    Console.WriteLine(animals);

    animals.Add(16, "cat");
    Console.WriteLine(animals);

    animals.Remove(8);
    Console.WriteLine(animals);

    Console.WriteLine(animals.At(11));

    animals.RemoveWithTag("dog");
    Console.WriteLine(animals);

    Console.WriteLine(animals.TagOf(16));

    Console.WriteLine("\nDone!\nPress any key to exit...");
    Console.ReadKey();
}

And the output is as you expected (except there is one item different, but that was a bug on your side):