哈希表的简单实现——线性探测

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>

using namespace std;

bool isprime(int n) {
    int lim = sqrt(n) + 1;
    for (int i = 2;i <= lim;i++)if (n%i == 0)return 0;
    return 1;
}

int nextprime(int n) {
    for (int i = n + 1;;i++)if (isprime(i))return i;
}

enum State
{
    EMPTY,
    EXIST,
    DELETE,
};

struct Node {
    string key;
    State s;
    Node(const string& key = "", State s = EMPTY) :key(key), s(s) {}
    Node& operator=(const Node&rhs) {
        key = rhs.key;
        s = rhs.s;
        return *this;
    }
};

int myhash(const string& key) {
    int hashVal = 0;
    for (size_t i = 0;i < key.length();i++)hashVal += 37 * hashVal + key[i];

    return hashVal;
}

class hashTable {
    typedef Node obj;
    friend void print(const hashTable& h) {
        for (int i = 0;i < h.size();i++)
            if (h._table[i].s == EXIST)cout << h._table[i].s << endl;
    }
private:
    vector<obj> _table;
    int num;
    int findEle(const string&);
    size_t size()const { return _table.size(); }//不加const限定符常引用对象无法调用此函数
    void chk_memory();
public:
    hashTable():num(0) {};
    bool find(const obj&);
    bool insert(const obj&);
    bool remove(const obj&);
};

inline
int hashTable::findEle(const string& key) {//查找是否存在
    if (num == 0 || size() == 0)return -1;
    int hv = myhash(key) % size();

    while (hv >= 0 && _table[hv].s != EMPTY) {//必须保证表不为空，不然可能死循环
        State cur = _table[hv].s;
        if (cur == DELETE || _table[hv].key != key) {
            hv++;//线性探测法
            if (hv == size())hv = 0;
            continue;
        }
        //已找到
        return hv;
    }
    return -1;//表示未找到
}

bool hashTable::find(const obj& o) {
    return findEle(o.key) != -1;
}

bool hashTable::remove(const obj&o) {
    int hv = findEle(o.key);
    if (hv == -1)return false;

    _table[hv].s = DELETE;
    num--;

    return true;
}

void hashTable::chk_memory() {
    if (num + 2 >= size()) {
        int newsize = (num == 0 ? 3 : 2 * num);
        newsize = nextprime(newsize);

        vector<obj> oldtable = _table;
        _table.resize(newsize);
        for (int i = 0;i < _table.size();i++)_table[i].s = EMPTY;
        for (int i = 0;i < oldtable.size();i++)
            if (oldtable[i].s == EXIST)_table[i] = oldtable[i];
    }
}

bool hashTable::insert(const obj&o) {
    if (find(o)) {
        cout << "已存在该键值,插入失败！" << endl;
        return false;
    }

    chk_memory();//保证有内存可插入
    
    int hv = myhash(o.key) % size();
    while (_table[hv].s == EXIST) {
        hv++;
        if (hv == size())hv = 0;
    }

    num++;
    _table[hv].key = o.key;
    _table[hv].s = EXIST;
    return true;
}

int main(void) {
    hashTable h;
    Node n(string("xixi"));
    h.insert(n);
    h.insert(n);
    if (h.find(n))cout << "hhh" << endl;
    h.remove(n);
    if (h.find(n))cout << "hhh" << endl;
    return 0;
}

没有经过严格测试，代码如上