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Method List explanation on a sort

Posted on 2013-10-23
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Last Modified: 2013-10-24
I have the following code and I'm trying to understand the Shuffle() method from the Deck class... It will be nice to get an explanation  from line by line of the suffle method line by line.

public void Shuffle()
        {
            Random rand = new Random();
            for (int i = cards.Count - 1; i > 0; i--)
            {
                int randomIndexg = rand.Next(i + 1);
                Card tempCard = cards[i];
                cards[i] = cards[randomIndexg];
                cards[randomIndexg] = tempCard;
            }
        }

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Class Deck
 public class Deck
    {
        #region Fields

        List<Card> cards = new List<Card>();

        #endregion

        #region Constructors

        /// <summary>
        /// Constructor
        /// </summary>
        public Deck()
        {
            // fill the deck with cards
            foreach (Suit suit in Enum.GetValues(typeof(Suit)))
            {
                foreach (Rank rank in Enum.GetValues(typeof(Rank)))
                {
                    cards.Add(new Card(rank.ToString(), suit.ToString()));
                }
            }
        }

        #endregion

        #region Properties

        /// <summary>
        /// Gets whether the deck is empty
        /// </summary>
        public bool Empty
        {
            get { return cards.Count == 0; }
        }

        #endregion

        #region Public methods

        /// <summary>
        /// Cuts the deck of cards at the given location
        /// </summary>
        /// <param name="location">the location at which to cut the deck</param>
        public void Cut(int location)
        {
            //int cutIndex = cards.Count - location;
            //List<Card> newCards = new List<Card>(cards.Count);
            //for (int i = cutIndex; i < cards.Count; i++)
            //{
            //    newCards.Add(cards[i]);
            //}
            //for (int i = 0; i < cutIndex; i++)
            //{
            //    newCards.Add(cards[i]);
            //}
            //cards = newCards;

            int cutIndex = cards.Count - location;
            Card[] newCards = new Card[cards.Count];
            cards.CopyTo(cutIndex, newCards, 0, location);
            cards.CopyTo(0, newCards, location, cutIndex);
            cards.Clear();
            cards.InsertRange(0, newCards);
        }

        /// <summary>
        /// Shuffles the deck
        /// 
        /// Reference: http://download.oracle.com/javase/1.5.0/docs/api/java/util/Collections.html#shuffle%28java.util.List%29
        /// </summary>
        public void Shuffle()
        {
            Random rand = new Random();
            for (int i = cards.Count - 1; i > 0; i--)
            {
                int randomIndex = rand.Next(i + 1);
                Card tempCard = cards[i];
                cards[i] = cards[randomIndex];
                cards[randomIndex] = tempCard;
            }
        }

        /// <summary>
        /// Takes the top card from the deck. If the deck is empty, returns null
        /// </summary>
        /// <returns>the top card</returns>
        public Card TakeTopCard()
        {
            if (!Empty)
            {
                Card topCard = cards[cards.Count - 1];
                cards.RemoveAt(cards.Count - 1);
                return topCard;
            }
            else
            {
                return null;
            }
        }

        /// <summary>
        /// Prints the contents of the deck
        /// </summary>
        public void Print()
        {
            foreach (Card card in cards)
            {
                Console.WriteLine(card.Rank + " of " + card.Suit);
            }
        }
        #endregion
    }

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Question by:yguyon28
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2 Comments
 

Author Comment

by:yguyon28
ID: 39595401
public void Shuffle()
        {
            Random rand = new Random();
            for (int i = cards.Count - 1; i > 0; i--)
            {
                int randomIndexg = rand.Next(i + 1);
                Card tempCard = cards[i];
                cards[i] = cards[randomIndexg];
                cards[randomIndexg] = tempCard;
            }
        }

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0
 
LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 500 total points
ID: 39595504
public void Shuffle()
{
    Random rand = new Random();                 // Create a new Random object. This will be used to create pseudo-random numbers.
    for (int i = cards.Count - 1; i > 0; i--)   // Create a loop to loop over deck. The loop will iterate cards.Count - 1 times.
    {
        int randomIndexg = rand.Next(i + 1);    // Get the next random integer less than i + 1 and greater than or equal to zero.
        Card tempCard = cards[i];               // Create a temporary variable that points to the Card object located at slot i of the cards List.
        cards[i] = cards[randomIndexg];         // Set slot i of the cards list to point to the Card object at slot randomIndexg of the cards List.
        cards[randomIndexg] = tempCard;         // Set slot randomIndexg of the cards list to point to the Card object that the temporary variable is point to
    }
}

// The net effect is that two cards swap positions. The positions swapped are i and randomIndexg

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