Question

The following is the inside of a method for collision detection while inserting into my own hash table. I’m working with small test numbers and trying to get my logic right, the variable hash is set to 0 and the table.length is 10.

 else
    {
                    //problem here   
        int initial=(hash-1)%table.length;


   while (table[hash]!=null)
        {
            hash+=1;
            System.out.println(initial);

            if (hash==table.length)
            {
                hash=0;
            }

            if (hash==initial)
            {
                System.out.println("FULL!");
                break;
            }

The variable initial needs to be the index BEFORE whatever my current one is (hash). My problem is if hash is 0, initial needs to be set to 9. I thought this would work but I’m getting -1 when hash is set to 0 for example. The first IF statement loops back to the first index if you for example started in the middle at 5 or something, the second one is for for when you’ve checked all indexes and they’re all full.

Answer 1

Since you use %, there is no risk of overflow, so you can just change the line to

int initial = (hash - 1 + table.length) % table.length;

to get around this problem.