hsp 哈希表 86-89

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class Main{
    public static void main(String args[]) {

        HashTab hashTab = new HashTab(7);

        Scanner scanner = new Scanner(System.in);
        String key = "";

        while(true) {
            System.out.println("add:添加雇员");
            System.out.println("list:显示雇员");
            System.out.println("find:查找雇员");
            System.out.println("delete:删除雇员");
            System.out.println("exit:退出系统");
            key = scanner.next();

            switch(key) {
                case "add":
                    System.out.println("输入id");
                    int id = scanner.nextInt();
                    System.out.println("输入名字");
                    String name = scanner.next();
                    Emp emp = new Emp(id, name);
                    hashTab.add(emp);
                    break;
                case "list":
                    hashTab.list();
                    break;
                case "find":
                    System.out.println("请输入要查找的id");
                    id = scanner.nextInt();
                    hashTab.findById(id);
                    break;
                case "delete":
                    System.out.println("请输入要删除的id");
                    id = scanner.nextInt();
                    hashTab.delete(id);
                    break;
                case "exit":
                    scanner.close();
                    System.exit(0);
            }
        }
    }




}

class HashTab {
    private LinkedList[] table;
    private int size;

    public HashTab(int size) {
        this.size = size;
        //注意！！这里只是初始化了数组，为数组分配了空间，数组的每个元素还是默认值
        //如果数组的元素是引用类型，它的默认值就是null
        //如果没有用for循环为数组的每个元素分配空间初始化，67行就会报空指针异常
        table = new LinkedList[size];

        //初始化数组的每个元素，为它们分配空间
        for(int i = 0; i < size; i++) {
            table[i] = new LinkedList();
        }
    }

    public int hash(int id) {
        return id % size;
    }

    public void add(Emp emp) {
        int index = hash(emp.id);
        table[index].add(emp);
    }

    //根据输入的id，查找雇员
    public void findById(int id) {

        int index = hash(id);
        Emp emp = table[index].findById(id);
        if(emp == null) {
            System.out.println("在哈希表中，没有查找到该雇员");
        } else {
            System.out.printf("在[%d]链表中查找到该id=%d的雇员信息\n", index, id);
        }
    }

    public void delete(int id) {
        int index = hash(id);
        boolean flag = table[index].delete(id);
        if(flag) {
            System.out.println("删除成功~");
        } else {
            System.out.println("删除失败");
        }
    }

    public void list() {
        for(int i = 0; i < size; i++) {
            table[i].list(i);
        }
    }
}

class LinkedList {
    private Emp head;

    public void add(Emp emp) {
        if(head == null) {
            head = emp;
            return;
        }

        Emp tmp = head;
        while(true) {
            if(tmp.next == null) {
                break;
            }
            tmp = tmp.next;
        }

        tmp.next = emp;
    }

    //根据id查找雇员
    //如果查找到，就返回那个对象，如果没找到，就返回null
    public Emp findById(int id) {
        if(head == null) {
            System.out.print("链表为空，");
            return null;
        }

        Emp tmp = head;
        while(true) {
            if(tmp.id == id) {
                break;
            }
            if(tmp.next == null) {
                tmp = null;
                break;
            }
            tmp = tmp.next;
        }

        return tmp;
    }

    //根据id删除雇员
    //如果找到，就返回true，如果没找到，就返回false
    public boolean delete(int id) {
        if(head == null) {
            System.out.print("链表为空，");
            return false;
        }

        Emp tmp = head;
        boolean flag = false; //标志是否找到待删除雇员，初始默认没找到
        while(true) {
            if(tmp.id == id) {
                flag = true;
                break;
            }
            if(tmp.next == null) {
                break;
            }
            tmp = tmp.next;
        }

        if(flag) {
            tmp.id = tmp.next.id;
            tmp.name = tmp.next.name;
            tmp.next = tmp.next.next;
        } else {
            System.out.print("没有查找到该雇员，");
        }

        return flag;
    }

    public void list(int no) {
        if(head == null) {
            System.out.println("[" + no + "]链表为空");
            return;
        }

        Emp tmp = head;
        System.out.print("[" + no + "]链表：");
        while(true) {
            System.out.printf("-> id = %d, name = %s\t", tmp.id, tmp.name);
            if(tmp.next == null) {
                break;
            }
            tmp = tmp.next;
        }
        System.out.println();
    }
}

class Emp {
    public int id;
    public String name;
    public Emp next;

    public Emp(int id, String name) {
        this.id = id;
        this.name = name;
    }

}