Check for missing number in sequence

Question

I have an List which contains 1,2,4,7,9 for example.

I have a range from 0 to 10.

Is there a way to determine what numbers are missin

Answer 1

Using Unity i have tested two solutions on set of million integers. Looks like using Dictionary and two "for" loops gives better result than Enumerable.Except

FindMissing1 Total time: 0.1420 (Enumerable.Except)
FindMissing2 Total time: 0.0621 (Dictionary and two for loops)

public static class ArrayExtension
{
    public static T[] FindMissing1(T[] range, T[] values)
    {
        List result = Enumerable.Except(range, values).ToList();
        return result.ToArray();
    }

    public static T[] FindMissing2(T[] range, T[] values)
    {
        List result = new List();
        Dictionary hash = new Dictionary(values.Length);
        for (int i = 0; i < values.Length; i++)
            hash.Add(values[i], values[i]);

        for (int i = 0; i < range.Length; i++)
        {
            if (!hash.ContainsKey(range[i]))
                result.Add(range[i]);
        }

        return result.ToArray();
    }
}

public class ArrayManipulationTest : MonoBehaviour
{
    void Start()
    {
        int rangeLength = 1000000;
        int[] range = Enumerable.Range(0, rangeLength).ToArray();
        int[] values = new int[rangeLength / 5];
        int[] missing;
        float start;
        float duration;

        for (int i = 0; i < rangeLength / 5; i ++)
            values[i] = i * 5;

        start = Time.realtimeSinceStartup;
        missing = ArrayExtension.FindMissing1(range, values);
        duration = Time.realtimeSinceStartup - start;
        Debug.Log($"FindMissing1 Total time: {duration:0.0000}");

        start = Time.realtimeSinceStartup;
        missing = ArrayExtension.FindMissing2(range, values);
        duration = Time.realtimeSinceStartup - start;
        Debug.Log($"FindMissing2 Total time: {duration:0.0000}");
    }
}