NumberTextualRepresentation.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MyLeetCodeJourney
{
    internal class NumberTextualRepresentation
    {
        private readonly Dictionary<int, string> namedNumbers = new()
        {
            {0, "Zero"},
            {1, "One"},
            {2, "Two"},
            {3, "Three"},
            {4, "Four"},
            {5, "Five"},
            {6, "Six"},
            {7, "Seven"},
            {8, "Eight"},
            {9, "Nine"},
            {10, "Ten"},
            {11, "Eleven"},
            {12, "Twelve"},
            {13, "Thirteen"},
            {14, "Fourteen"},
            {15, "Fifteen"},
            {16, "Sixteen"},
            {17, "Seventeen"},
            {18, "Eighteen"},
            {19, "Nineteen"},
            {20, "Twenty"},
            {30, "Thirty"},
            {40, "Forty"},
            {50, "Fifty"},
            {60, "Sixty"},
            {70, "Seventy"},
            {80, "Eighty"},
            {90, "Ninety"}
        };

        private readonly Dictionary<int, string> divideNumbers = new() { { 1000000000, "Billion" }, { 1000000, "Million" }, { 1000, "Thousand" }, { 100, "Hundred" } };

        public NumberTextualRepresentation() { }

        /// <summary>
        /// Returns a text name of a given number.
        /// </summary>
        /// <param name="number">a number between 0 - 1 Billion</param>
        /// <returns></returns>
        public string NumberToString(int number)
        {
            string constructedName = string.Empty;
            foreach(var divider in divideNumbers.Keys)
            {

                if(number / divider  != 0)
                {
                    constructedName += NumberToString(number / divider) + divideNumbers[divider];
                    number %= divider;
                }
            }

            // in case that number is less than 100.
            if (number != 0)
            {
                constructedName += UnderOneHundredString(number);
            }

            return constructedName;
            
        }

        private string UnderOneHundredString(int number)
        {
            if (namedNumbers.TryGetValue(number, out var name))
            {
                return name;
            }

            string constructedName = string.Empty;
            constructedName += namedNumbers[number - number % 10];
            if(number % 10 != 0)
            {
                constructedName += namedNumbers[number % 10];
            }


            return constructedName;
        }
    }
}