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Thread: hash table probes

  1. #1
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    Default hash table probes

    working on hash table assignment. searching the table for 100 different keys. trying to keep track of total # of probes (linear) for all successful searches and same for failures. also tracking total # of successful searches. my table has variables numberProbesSuccess, numberProbesFail, and totalSuccess.

    my method "find" is not incrementing these proper

       public void find(int key)    // find item with key
          {
    		int numberProbes = 0;
          int hashVal = hashFunc(key);  // hash the key
     
          while(hashArray[hashVal] != null)  // until empty cell,
             {                               // found the key?
    			numberProbes++;
             if(hashArray[hashVal].getKey() == key)
    				{
    				numberProbesSuccess += numberProbes;  // update # of probes for success
    				totalSuccess++;
    //				System.out.println("Number of probes: " + numberProbes);
                return;   // yes, return item
    				}
    			else
    				{
             	hashVal++;                 // go to next cell
             	hashVal %= arraySize;      // wraparound if necessary
             	}
    			} // end while
    		numberProbes++;
    //		System.out.println("Number of probes: " + numberProbes);
    		numberProbesFail += numberProbes;           // update # of probes for failure
          return;                  // can't find item
          }


  2. #2
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    Default Re: hash table probes

    numberProbesSuccess += numberProbes;

    I assume that numberProbes hold the total probes (successful and unsuccessful). If so why are you incrementing numberProbesSuccess by this number? If you have a successful probe, by what value should numberProbesSuccess be incremented by?
    Improving the world one idiot at a time!

  3. #3
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    Default Re: hash table probes

    unsuccesful if while loop finds null. numberProbes can be used for successul searches (if the "if" finds == key) in which case the method returns OR for unsuccessful in case null is found, then numberProbes is assigned to numberProbesFail.

  4. #4
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    Default Re: hash table probes

    also, numberProbes resets with each of the 100 calls to find()

  5. #5
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    Default Re: hash table probes

    OK nevermind - I figured it out. This test is being run using different load factors .1, .2, ... , .9

    All of the empirical data matches up with the theoretical (avg # probes for searches), EXCEPT for the .9 load factor. It blows up big time (way more than the theoretical).

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