using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        //keys added out of order

        var d = new KeyLengthSortedDictionary(){

            {"aaa","3"},

            {"aaaa","4"},

            {"bbbb","4"},

            {"a","1"},

            {"aaaaa","5"}

        };

        //keys enumerated over are in order

        foreach(string key in d.Keys) {

            Console.WriteLine("Key {0} Value {1}", key, d[key]);

​

        }       

        Console.WriteLine("Decending...");

        //keys added out of order

        var dd = new KeyLengthSortedDecendingDictionary(){

            {"aaa","3"},

            {"aaaa","4"},

            {"bbbb","4"},

            {"a","1"},

            {"aaaaa","5"}

        };

        //keys enumerated over are in order

        foreach(string key in dd.Keys) {

            Console.WriteLine("Key {0} Value {1}", key, dd[key]);

​

        }   

    }

​

    public class KeyLengthSortedDictionary : SortedDictionary<string, string>

    {

        private class StringLengthComparer : IComparer<string>

        {

            public int Compare(string x, string y)

            {

                if (x == null) throw new ArgumentNullException(nameof(x));

                if (y == null) throw new ArgumentNullException(nameof(y));

                var lengthComparison = x.Length.CompareTo(y.Length);

                return lengthComparison == 0 ? string.Compare(x, y, StringComparison.Ordinal) : lengthComparison;

            }

        }

        public KeyLengthSortedDictionary() : base(new StringLengthComparer()) { }   

    }

    public class KeyLengthSortedDecendingDictionary : SortedDictionary<string, string>

    {

        private class StringLengthComparer : IComparer<string>

        {

            public int Compare(string x, string y)

            {

                if (x == null) throw new ArgumentNullException(nameof(x));

                if (y == null) throw new ArgumentNullException(nameof(y));

                var lengthComparison = x.Length.CompareTo(y.Length) * -1;

                return lengthComparison == 0 ? string.Compare(x, y, StringComparison.Ordinal) : lengthComparison;

            }

        }

        public KeyLengthSortedDecendingDictionary() : base(new StringLengthComparer()) { }   

    }

}