lintcode-easy-Hash Function

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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.

class Solution {
    /**
     * @param key: A String you should hash
     * @param HASH_SIZE: An integer
     * @return an integer
     */
    public int hashCode(char[] key,int HASH_SIZE) {
        // write your code here
        if(key == null || key.length == 0)  
            return 0;
        
        long factor = 1;
        long result = 0;
        
        for(int i = key.length - 1; i >= 0; i--){
            result += (((int) key[i]) * factor) % HASH_SIZE;
            factor = (factor * 33) % HASH_SIZE;
            
        }
        
        result %= HASH_SIZE;
        
        return (int) result;
    }
};

lintcode-easy-Hash Function

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原文地址：http://www.cnblogs.com/goblinengineer/p/5215685.html