西南交通大学数据结构第八次实验--哈希表的建立与查找

实验内容及要求：

编写控制台应用程序，提供以下菜单项：

1. 插入关键字
2. 删除关键字
3. 查找关键字
4. 结束程序

其中，“插入关键字”是指从键盘输入一个关键字，将关键字插入哈希表中，若插入的关键字已存储于哈希表中，则插入失败，显示提示信息；若插入关键字数目已超过哈希表设计容量，则插入失败，显示提示信息；其它情况则插入成功，显示提示信息。程序初始运行时，哈希表为空，通过插入多个关键字建立哈希表。

“删除关键字”是指从键盘输入一个关键字，若在哈希表中查找成功，则将关键字从哈希表中删除；若查找失败，显示提示信息。

“查找关键字”是指从键盘输入一个关键字，在哈希表中查找，显示查找成功与失败的提示信息。

已知哈希函数H(K)=K mod m，其中m为哈希表长度（程序中m应不小于10）。可选择用二次探测再散列或链地址法解决冲突。若选用二次探测再散列，装填因子设为0.8；若选用链地址法，要求哈希表允许的关键字最大数目为2m。

提示：选用二次探测再散列时，空闲元素位置应存入“哑元素”占位，以标识元素位置空闲。

实验目的：掌握哈希表的建立与查找。

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PS：本代码采用链地址法。并且只经过了简要测试，可能存在bug

友情链接：同学自己搭建的博客网站https://bzyl.site

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#include 

using namespace std;


typedef struct Node {
    int data = 0;
    bool flag = false;
    Node* next = nullptr;
}Node;


class Menu {
private:
    Node* hash_map;
    int map_length;
    int cur_length;

    int HashFunction(int key) const;

    static void DisplayMenu();

    void Insert();

    void Delete();

    void LookUp();

public:
    explicit Menu(int length);

    void Start();

    ~Menu();

};

Menu::Menu(int length) {
    while (length <= 10) {
        cout << "Too short! Retype a number which is more than 10!" << endl;
        cin >> length;
    }
    map_length = length;
    hash_map = new Node[length];
    cur_length = 0;
}

Menu::~Menu() {
    delete hash_map;
}

int Menu::HashFunction(int key) const {
    return key % (2 * map_length);
}

void Menu::DisplayMenu() {
    cout << "------------------------------------------" << endl;
    cout << "            1.Insert key word             " << endl;
    cout << "            2.Delete key word             " << endl;
    cout << "            3.Look up key word            " << endl;
    cout << "            4.Exit                        " << endl;
    cout << "------------------------------------------" << endl;
}

void Menu::Insert() {
    int key;
    cout << "Please enter a key: ";
    cin >> key;
    int position = HashFunction(key);
    auto p = &hash_map[position];
    if (cur_length + 1 >= map_length) {
        cout << "The current length has exceed allowed length!" << endl;
        cout << "Insertion failed!" << endl;
        return ;
    }
    if (p->flag) {
        if (p->data == key) {
            cout << "Insertion failed! Key exists!" << endl;
            return ;
        } else {
            while(p) {
                if (p->data == key) {
                    cout << "Insertion failed! Key exists!" << endl;
                    return ;
                } else {
                    if (p->next) {
                        p = p->next;
                    } else {
                        auto new_node = new Node;
                        new_node->data = key;
                        new_node->flag = true;
                        p->next = new_node;
                        cur_length++;
                        break;
                    }
                }
            }
        }
    } else {
        hash_map[position].data = key;
        hash_map[position].flag = true;
        cur_length++;
    }
    cout << "Insertion " << key << " succeed!" << endl;
}

void Menu::Delete() {
    int key;
    cout << "Please enter the key: ";
    cin >> key;
    int position = HashFunction(key);
    auto p1 = &hash_map[position];
    auto p2 = &hash_map[position];
    bool flag = false;
    while (p1->flag && p1) {
        if (p1->data == key) {
            if (p1 == p2) {
                if (p1->next) {
                    hash_map[position] = *p1->next;
                    flag = true;
                    break;
                } else {
                    p1->flag = false;
                    p1->data = 0;
                    flag = true;
                    break;
                }
            } else {
                if (p1->next) {
                    p2->next = p1->next;
                    p1->next = nullptr;
                    flag = true;
                    delete p1;
                    break;
                } else {
                    p2->next = nullptr;
                    flag = true;
                    delete p1;
                    break;
                }
            }
        } else {
            p1 = p1->next;
            p2 = p1;
        }
    }
    if (!flag) {
        cout << "Delete failed!" << key << " doesn't exist!" << endl;
    } else {
        cout << "Delete succeed!" << endl;
    }
}

void Menu::LookUp() {
    int key;
    cout << "Please enter the key: " << endl;
    cin >> key;
    int position = HashFunction(key);
    auto p1 = &hash_map[position];
    int flag = false;
    while (p1->flag && p1) {
        if (p1->data == key) {
            flag = true;
            break;
        } else {
            p1 = p1->next;
        }
    }
    if (flag) {
        cout << "Look up succeed!" << endl;
        cout << key << " is in the hash map!" << endl;
    } else {
        cout << "Look up failed!" << endl;
        cout << key << " doesn't exist!" << endl;
    }
}

void Menu::Start() {
    int choice;
    while (true) {
        DisplayMenu();
        cin >> choice;
        switch (choice) {
            case 1:
                Insert();
                break;
            case 2:
                Delete();
                break;
            case 3:
                LookUp();
                break;
            case 4:
                exit(0);
            default:
                break;
        }
    }
}

int main() {
    cout << "Please enter the max number the hash map can restore: " << endl;
    int number;
    cin >> number;
    Menu menu(number);
    menu.Start();
    return 0;
}