Advent of Code 2020 Day 15 Parts 1 and 2

//Advent of Code 2020 Day 15 Parts 1 and 2 solution by Mike LeSauvage

using System.Collections;
using UnityEngine;
using System.Linq;

public class MemoryGame : MonoBehaviour
{
    //Store the spoken numbers in a hashtable.
    //Format:
    //  - Each entry in the hash is a 2-element array storing the last two numbers that were spoken.
    //  - When the number hasn't been spoken, there is no entry for that number in the hashtable.
    //  - When first spoken, the array is initialized to [-1, turn spoken].
    //  - When spoken again, older turns are pushed to the left.
    Hashtable spokenNumbers = new Hashtable();
    int numTurns = 30000000;
    int[] puzzleInputSeedNumbers = { 0, 5, 4, 1, 10, 14, 7 };
    int[] testSeedNumbers = { 0, 3, 6 };

    //Start is part of Unity; put code where it makes sense for you!
    void Start()
    {
        int[] seedNumbers = puzzleInputSeedNumbers;
        int turn = 1;

        //Speak the seed numbers.
        //NOTE: This approach assumes seed numbers are not duplicated! (Might work but not considered/tested)
        for(; turn<=seedNumbers.Length; turn++)
        {
            SpeakNumber(seedNumbers[turn - 1], turn);
        }

        int prevSpoken = seedNumbers.Last();

        //Iterate through to the final number.
        for (; turn <= numTurns; turn++)
        {
            int speak = GetTurnSinceLastSpoken(prevSpoken, turn);
            SpeakNumber(speak, turn);
            prevSpoken = speak;
        }

        Debug.Log($"Last spoken on turn {turn-1} was {prevSpoken}");
    }

    int GetTurnSinceLastSpoken(int num, int currentTurn)
    {
        int[] turnsSpoken = (int[])spokenNumbers[num];  //Get the 2D array from the hash. Entry is expected to exist!

        //Only one in the list! Was first spoken last turn
        if (turnsSpoken[0] == -1)
        {
            return 0;
        }

        //Two in the list. [1] has the entry from last turn... look at [0] for the previous entry.
        int lastTurnSpoken = turnsSpoken[0];
        return currentTurn-1 - lastTurnSpoken; //Extra -1 as we're considering the prevous turn as the starting point.
    }

    //If the number hasn't been spoken before, creates a hash entry for it as
    //a 2D array and seeds it with [-1, currentTurn].
    //It it has been spoken before, moves the recent entry to [0] and adds
    //currentTurn to [1] so the most recent turn the number was spoken is at [1].
    void SpeakNumber(int num, int currentTurn)
    {
        int[] turnsSpoken = (int[])spokenNumbers[num];

        if (turnsSpoken == null)
        {
            turnsSpoken = new int[2] { -1, currentTurn };
            spokenNumbers[num] = turnsSpoken;
        }
        else
        {
            turnsSpoken[0] = turnsSpoken[1];
            turnsSpoken[1] = currentTurn;
        }
    }

}