算法导论11.2散列表Hash tables链式法解决碰撞11.3.1除法散列法

11.2是第11章的主要内容，11章叫散列表(Hash Tables)11.2也叫散列表(Hash Tables)

11.3节讲散列函数(比如除尘散列法)，11.4节讲处理碰撞的另外一种方法区别于链式法技术

散列技术，有两个事情要做，一是先哈希函数(11.3)，二是解决碰撞技术(11.2链式解决碰撞,11.4开放寻址解决碰撞）。

/*
 * IA_11.2ChainedHash.h
 *
 *  Created on: Feb 13, 2015
 *      Author: sunyj
 */
 
#ifndef IA_11_2CHAINEDHASH_H_
#define IA_11_2CHAINEDHASH_H_
 
#include <iostream>
#include <string.h>
 
#include "IA_10.2LinkedLists.h"
 
// CHAINED-HASH-INSERT(T, x)
// insert x at the head of list T[h(x.key)]
 
// CHAINED-HASH-SEARCH(T, k)
// search for an element with key k in list T[h(k)]
 
// CHAINED-HASH-DELETE(T, x)
// delete x from the list T[h(x.key)]
 
template <class T> class ChainedHashTable {
public:
    ChainedHashTable(int64_t const n) : size(n)
    {
        data = new LinkedList<int64_t, T>[n]();
    }
    ~ChainedHashTable() {}
    int64_t HashFunc(int64_t const key)
    {
        return key % size;
    }
    Node<int64_t, T>* search(int64_t const key)
    {
        return data[HashFunc(key)].search(key);
    }
    // the user of this class, has to invoke search first
    // this interface assume that x was not in the hash table
    void insert(Node<int64_t, T>* x)
    {
        (data[HashFunc(x->key)]).insert(x);
    }
    void del(Node<int64_t, T>* x)
    {
        data[HashFunc(x->key)].del(x);
    }
    void print(int64_t key)
    {
        data[HashFunc(key)].print();
    }
private:
    LinkedList<int64_t, T>* data;
    int64_t const size;
};
 
#endif /* IA_11_2CHAINEDHASH_H_ */

/*
 * IA_11.2ChainedHash.cpp
 *
 *  Created on: Feb 12, 2015
 *      Author: sunyj
 */
 
#include "IA_11.2ChainedHash.h"
 
int main()
{
    /*
     * A prime not too close to an exact power of 2 is often a good choice for m. For
example, suppose we wish to allocate a hash table, with collisions resolved by
chaining, to hold roughly n = 2000 character strings, where a character has 8 bits.
We don't mind examining an average of 3 elements in an unsuccessful search, and
so we allocate a hash table of size m = 701. We could choose 701 because
it is a prime near 2000=3 but not near any power of 2.
     */
    ChainedHashTable<int64_t> table(701); // The division method,
 
    Node<int64_t, int64_t> node1(1, 100);
    Node<int64_t, int64_t> node4(4, 400);
    Node<int64_t, int64_t> node16(16, 1600);
    Node<int64_t, int64_t> node9(9, 900);
    if (nullptr == table.search(node1.key))
    {   // search before insert
        table.insert(&node1);
    }
    else
    {
        std::cout << "node1 already exist" << std::endl;
    }
    if (nullptr == table.search(node1.key))
    {
        table.insert(&node1);
    }
    else
    {
        std::cout << "node1 already exist" << std::endl;
    }
    table.insert(&node4);
    table.insert(&node16);
    table.insert(&node9);
    table.print(4);
    Node<int64_t, int64_t> node25(25, 2500);
    table.insert(&node25);
    table.print(16);
    // search before del, or you are clearly sure that, there are this node exist.
    // if node1 is not exist, and you invoke del, program will crush
    table.del(&node1);
    table.print(9);
    Node<int64_t, int64_t>* tmp;
    tmp = table.search(9);
    table.del(tmp);
    table.print(9);
    return 0;
}