哈希表

来源：互联网发布：centos 中英输入法转换编辑：程序博客网时间：2024/06/16 12:04
哈希表又叫散列表，关键值通过哈希函数映射到数组上，查找时通过关键值直接访问数组。
#include <iostream>#include <string>using namespace std;class HashTable {private:    string *elem;    int size;public:    HashTable() {        size = 2000;        elem = new string[size];        for (int i = 0; i < size; i++) {            elem[i] = "#";        }    }    ~HashTable() {        delete[] elem;    }    int hash(string& index) {        int code = 0;        for (size_t i = 0; i < index.length(); i++) {            code = (code * 256 + index[i] + 128) % size;        }        return code;    }    bool search(string& index, int& pos, int& times) {        pos = hash(index);        times = 0;        while (elem[pos] != "#" && elem[pos] != index) {            times++;            if (times < size) {                pos = (pos + 1) % size;            } else {                return false;            }        }        if (elem[pos] == index) {            return true;        } else {            return false;        }    }    int insert(string& index) {        int pos, times;        if (search(index, pos, times)) {            return 2;        } else if (times < size / 2) {            elem[pos] = index;            return 1;        } else {            recreate();            return 0;        }    }    void recreate(){        string * temp_elem;        temp_elem = new string[size];        for(int i=0;i<size;i++){            temp_elem[i]=elem[i];        }        int copy_size=size;        size*=2;        delete[] elem;        elem = new string[size];        for(int i=0;i<size;i++){            elem[i]="#";        }        for(int i=0;i<copy_size;i++){            if(temp_elem[i]!="#"){                insert(temp_elem[i]);            }        }        delete[] temp_elem;    }};int main() {    HashTable hashtable;    string buffer;    int n;    cin >> n;    for (int i = 1; i <= n; i++) {        cin >> buffer;        int ans = hashtable.insert(buffer);        if (ans == 0) {            cout << "insert failed!" << endl;        } else if (ans == 1) {            cout << "insert success!" << endl;        } else if (ans == 2) {            cout << "It already exists!" << endl;        }    }    int temp_pos, temp_times;    cin >> buffer;    if (hashtable.search(buffer, temp_pos, temp_times)) {        cout << "search success!" << endl;    } else {        cout << "search failed!" << endl;    }    return 0;}
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