1. h(k) = k mod m
its is really bad in the practical. if m = even and k is all even....
( m is size of hash table,
)
2. multiplication method. 好一点
a multiplice the k and sum mod 2^w w is the bit length integer. two power of two.
3. Universal hashing.
h(k) = [(a*k + b) mod p] mod m p is a prime number. p>m a,b random from 0-p-1
h(k1)=h(k2) probability <= 1/m
原文：http://www.cnblogs.com/leetcode/p/3940716.html