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Thread: vector

  1. #1
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    Question vector

    Hai

    Can anybody help me out to write a java program which identifies a duplicate value in a Vector
    please send me the code along with the examples.

    links are also welcomed

    Thanks in Advance
    Srinivas Kundan


  2. #2
    Super Moderator Json's Avatar
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    Default Re: vector

    Vector as in java.util.Vector<E> ?

    Have a google at it, its not that hard.

    // Json

  3. #3
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    Default Re: vector

    Yeah pretty simple, still

    Vector<String> strVect = new Vector<String>();

    for(String str : strVect) {
    if(strVect.contains(str)) {
    return true;
    }
    }

    return false;
    Acumen
    Lucid forums

  4. #4
    Super Moderator Json's Avatar
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    Default Re: vector

    That for loop seems redundant to me, you might as well remove that. By the way Vectors are more or less also redundant as you have ArrayList these days. Only reason for the Vector might be concurrency but then again it's not fully thread safe using Vector anyways.

    // Json

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    Default Re: vector

    Hi Json,

    Appreciate you pointing that. I totally understand that I am doing in O(n^2) and we can do using hashing in O(n) space and O(n) time OR O(nlogn) time and constant space by sorting. But that is all algorithms. Looking at the question, it clearly shows the person who asked question must be new to Java, so I replied trivial solution.
    In fact I think you can do it by just exchanging across the data structures in Java also I guess.

    Nice to met you Json.

    Acumen
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  6. #6
    Super Moderator Json's Avatar
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    Default Re: vector

    Nice to meet you too.

    I understand what you did but as well as teaching people how to do things its also nice to comment on bad practices I believe.

    // Json

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    Default Re: vector

    Totally correct, please don't get me wrong Just explaining reason why I replied that way. Feedback of any kind is always welcome, that is the way we grow as people

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    Default Re: vector

    Agree

    // Json

  9. #9
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    Default Re: vector

    whenever you try to add an element to this hash table, it will return false if a duplicate is found. Note that a duplicate is compared by .equals method of Object. Should be almost O(n) running time, unless there are large clusters.
    public class HashTable<E>
    {
        int                     size;
        ArrayList<ArrayList<E>> hash;
     
        /**
         * Creates an empty hash table with a given size
         * 
         * @param size
         */
        public HashTable (int size)
        {
            this.size = size;
            hash = new ArrayList<ArrayList<E>>();
            hash.ensureCapacity(size);
            for (int i = 0; i < size; i++)
            {
                hash.add(new ArrayList<E>());
            }
        }
     
        /**
         * Adds an element to the hash table.<br>
         * 
         * @param element
         * @return true if successfully added, false otherwise (duplicate)
         */
        public boolean add (E element)
        {
            if (hash.contains(element))
            {
                    return false;
            }
            hash.get(hashFunction(element.toString())).add(element);
            return true;
        }
     
        /**
         * Determines if an element is in the hash table.
         * 
         * @param element
         * @return true if found, false otherwise
         */
        public boolean contains (E element)
        {
            // get a list of those that hash to the same value
            ArrayList<E> list = hash.get(hashFunction(element.toString()));
            for (int i = 0; i < list.size(); i++)
            {
                // try to find the element from the list
                if (list.get(i).equals(element))
                {
                    return true;
                }
            }
            // didn't find element
            return false;
        }
     
        /**
         * Gets an element from the hash, if it exists.<br>
         * If duplicates (toString() matches), the first is returned.
         * 
         * @return the item (null if none)
         */
        public E get (E element)
        {
            // get a list of those that hash to the same value
            ArrayList<E> list = hash.get(hashFunction(element.toString()));
            for (int i = 0; i < list.size(); i++)
            {
                // find one who's to string matches, remove and return
                if (list.get(i).equals(element))
                {
                    return list.get(i);
                }
            }
            // didn't find any, return
            return null;
        }
     
        /**
         * Removes an element from the hash, if it exists.<br>
         * If duplicates (toString() matches), the first is removed.
         * 
         * @return the removed item (null if none)
         */
        public E remove (E element)
        {
            // get a list of those that hash to the same value
            ArrayList<E> list = hash.get(hashFunction(element.toString()));
            for (int i = 0; i < list.size(); i++)
            {
                // find one who's to string matches, remove and return
                if (list.get(i).equals(element))
                {
                    return list.remove(i);
                }
            }
            // didn't find any, return
            return null;
        }
     
        /**
         * @return the size of the hash table array
         */
        public int size ()
        {
            return size;
        }
     
        /**
         * Takes a string representation of an object and hashes it.
         * 
         * @param str
         * @return
         */
        private int hashFunction (String str)
        {
            int hashval = 0;
            for (int i = 0; i < str.length(); i++)
            {
                hashval = 37 * hashval + str.charAt(i);
            }
            hashval %= size;
            if (hashval < 0)
                hashval += size;
            return hashval;
        }
    }

  10. The Following User Says Thank You to helloworld922 For This Useful Post:

    JavaPF (August 12th, 2009)