turing-machine/Implementation/Core/Tape.cs

using System.Collections.Generic;

namespace TuringMachine.Core
{
    public class Tape
    {
        private readonly Dictionary<int, char> _data = new();
        private readonly char _blankSymbol;

        public int MinIndex { get; private set; } = 0;
        public int MaxIndex { get; private set; } = 0;

        public Tape(char blankSymbol = '_')
        {
            _blankSymbol = blankSymbol;
        }

        public char this[int index]
        {
            get => _data.TryGetValue(index, out char value) ? value : _blankSymbol;
            set
            {
                if (value == _blankSymbol)
                {
                    _data.Remove(index);
                }
                else
                {
                    _data[index] = value;
                    
                    // Track min/max indices
                    if (_data.Count == 1)
                    {
                        MinIndex = index;
                        MaxIndex = index;
                    }
                    else
                    {
                        if (index < MinIndex) MinIndex = index;
                        if (index > MaxIndex) MaxIndex = index;
                    }
                }
            }
        }

        public void Clear()
        {
            _data.Clear();
            MinIndex = 0;
            MaxIndex = 0;
        }

        public IEnumerable<int> DefinedIndices => _data.Keys;
    }
}