Hash table size

• By "size" of the hash table we mean how many slots or buckets it has
  
• Choice of hash table size depends in part on choice of hash function, and collision resolution strategy
  
• But a good general “rule of thumb” is:
• The hash table should be an array with length about 1.3 times the maximum number of keys that will actually be in the table, and
• Size of hash table array should be a prime number
  
  
• So, let M = the next prime larger than 1.3 times the number of keys you will want to store in the table, and create the table as an array of length M
  
  
• (If you underestimate the number of keys, you may have to create a larger table and rehash the entries when it gets too full; if you overestimate the number of keys, you will be wasting some space)