哈希表（HashTable）

1.整型哈希函数的设计
小范围正整数直接使用
小范围负整数整体进行偏移
大整数，通常做法是"模一个素数"

2.浮点型哈希函数的设计
转成整型进行处理

3.字符串哈希函数的设计
转成整型进行处理

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简单变形优化

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防止整型溢出优化

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具体代码实现

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复合类型哈希函数的设计
转成整型进行处理

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哈希函数的设计原则

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哈希冲突的处理
链地址法

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开放地址法之线性探测

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开放地址法之平方探测

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开放地址法之二次哈希

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哈希表的动态空间处理

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实现哈希表的业务逻辑

import java.util.TreeMap;

public class HashTable {

    private final int[] capacity
            = {53, 97, 193, 389, 769, 1543, 3079, 6151, 12289, 24593,
            49157, 98317, 196613, 393241, 786433, 1572869, 3145739, 6291469, 12582917,
            25165843, 50331653, 100663319, 201326611, 402653189, 805306457, 1610612741};
    private static final int upperTol = 10;
    private static final int lowerTol = 2;
    private int capacityIndex = 0;
    private TreeMap[] hashTable;
    private int M;
    private int size;

    public HashTable() {

        this.M = capacity[capacityIndex];
        this.size = 0;
        hashTable = new TreeMap[M];
        for (int i = 0; i < M; i++) {
            hashTable[i] = new TreeMap<>();
        }
    }

    private int hash(K key) {
        return key.hashCode() & 0x7fffffff % M;
    }

    public void add(K key, V value) {

        TreeMap map = hashTable[hash(key)];

        if (map.containsKey(key)) {
            map.put(key, value);
        } else {
            map.put(key, value);
            size++;
            if (size >= upperTol * M && capacityIndex + 1 < capacity.length) {
                capacityIndex++;
                resize(capacity[capacityIndex]);
            }
        }
    }

    public V remove(K key) {

        TreeMap map = hashTable[hash(key)];

        V ret = null;
        if (map.containsKey(key)) {
            ret = map.remove(key);
            size--;
            if (size < lowerTol * M && capacityIndex - 1 >= 0) {
                capacityIndex--;
                resize(capacity[capacityIndex]);
            }
        }
        return ret;
    }

    public void set(K key, V value) {

        TreeMap map = hashTable[hash(key)];

        if (!map.containsKey(key)) {
            throw new IllegalArgumentException(key + "doesn't exist.");
        } else {
            map.put(key, value);
        }
    }

    public boolean contains(K key) {

        return hashTable[hash(key)].containsKey(key);
    }

    public V get(K key) {

        return hashTable[hash(key)].get(key);
    }

    private void resize(int newM) {

        TreeMap[] newHashTable = new TreeMap[newM];
        for (int i = 0; i < newM; i++) {
            newHashTable[i] = new TreeMap<>();
        }

        int oldM = M;
        M = newM;
        for (int i = 0; i < oldM; i++) {
            TreeMap map = hashTable[i];
            for (K key : map.keySet()) {
                newHashTable[hash(key)].put(key, map.get(key));
            }
        }

        this.hashTable = newHashTable;
    }

}