Re-sizing a Hash Table

Question

I am trying to re-size a hash table. I find that my logic is correct, but the code is all wrong. I know that when adding elements into a hash table you must consider the load factor, if the load factor is exceeded, the capacity doubles.

Example. Size = 3, Capacity = 5.
Load Factor = 5 * 0.75 = 3.75
If we add an element Size = 4, which exceeds the load factor, thus Capacity = 10. However, I am return the original Capacity.

/**
* size if load >.75 or < .5
*/
private void resize(int newCap)
{
  //   
   double capacity = buckets.length * 0.75;
   //System.out.println(capacity);
   if (currentSize > capacity) {
       int C = buckets.length * 2;
       newCap = C
       //System.out.println(C);
   }
}

/**
 * Gets the length of the array backing this HashSet
 * @return the length of the array backing this HashSet
 */
public int getCap()
{
  //
   int capac = buckets.cap
   resize(capac);
   return capac;
}

Is it not necessary in your hash table implementation to re-add every item stored in the table upon resize? — SimonT, Dec 04 '13 at 05:18
It is actually! I've been attack this problem incorrectly.. ahh thanks @SimonT — user3011391, Dec 04 '13 at 05:27

score 0 · Answer 1 · edited May 23 '17 at 12:16

newCap = C in method resize will not change the value of capac

You should be returning the newCap from resize method

/**
* size if load >.75 or < .5
*/
private int resize(int newCap)
{
  //   
   double capacity = buckets.length * 0.75;
   //System.out.println(capacity);
   if (currentSize > capacity) {
       int C = buckets.length * 2;
       return C;
       //System.out.println(C);
   }
   return newCap;
}

/**
 * Gets the length of the array backing this HashSet
 * @return the length of the array backing this HashSet
 */
public int getCap()
{
  //
   int capac = buckets.cap;
   capac = resize(capac);
   return capac;
}

In java, there is always pass-by-value. See a relevant discussion here

Edit: Changed the return type as rightly pointed out.

However; you cannot return a value from a method whose type is Void. — user3011391, Dec 04 '13 at 04:33

Re-sizing a Hash Table

1 Answers1