Hash function

In data structure Hash, hash function is used to convert a string(or any other type) into an integer smaller than hash size and bigger or equal to zero. The objective of designing a hash function is to "hash" the key as unreasonable as possible. A good hash function can avoid collision as less as possible. A widely used hash function algorithm is using a magic number 33, consider any string as a 33 based big integer like follow:

hashcode("abcd") = (ascii(a) * 333 + ascii(b) * 332 + ascii(c) *33 + ascii(d)) % HASH_SIZE 

                 = (97* 333 + 98 * 332 + 99 * 33 +100) % HASH_SIZE

                 = 3595978 % HASH_SIZE

here HASH_SIZE is the capacity of the hash table (you can assume a hash table is like an array with index 0 ~ HASH_SIZE-1).

Given a string as a key and the size of hash table, return the hash value of this key.

(A % C + B % C) % C = (A + B) % C;

public int hashCode(char[] key, int HASH_SIZE) {
        long result = 0;
        for (int i = 0; i < key.length; i++) {
            result = (result * 33 + (int) (key[i])) % HASH_SIZE;
        } 
        
        return (int) result;
    }