哈希表

package com.dai.hashtab;

import java.security.PublicKey;
import java.util.Scanner;

public class HashTabDemo {

    public static void main(String[] args) {
        //创建一个hash表
        HashTab hashTab = new HashTab(7);
        String key = "";
        Scanner scanner = new Scanner(System.in);
        while(true) {
            System.out.println("add: 添加雇员");
            System.out.println("list:显示雇员");
            System.out.println("exit: 退出系统");
            System.out.println("find: 查找雇员");
            
            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("请输入查找的id:");
                id = scanner.nextInt();
                hashTab.findEmpById(id);
                break;
            case "exit":
                scanner.close();
                System.exit(0);
            default:
                break;
            }
        }

    }

}
//创建哈希表
class HashTab{
    private EmpLinkedList[] empLinkedListArray;
    private int size;
    //构造器
    public HashTab(int size) {
        this.size = size;
        empLinkedListArray = new EmpLinkedList[size];
        //这里需要记得初始化每一个链表
        for(int i=0;i<size;i++) {
            empLinkedListArray[i] = new EmpLinkedList();
        }
        
    }
    //添加雇员
    public void add(Emp emp) {
        //根据Id,决定添加到哪条链表
        int empLinkedListNO = hashFun(emp.id);
        empLinkedListArray[empLinkedListNO].add(emp);
        
        
    }
    //遍历所有的链表
    public void list() {
        for(int i=0;i<size;i++) {
            empLinkedListArray[i].list(i);
        }
    }
    
    //根据输入的id查找雇员
    public void findEmpById(int id) {
        int empLinkedListNO = hashFun(id);
        Emp emp = empLinkedListArray[empLinkedListNO].findEmpById(id);
        if(emp != null) {
            System.out.printf("在第%d条链表中找到雇员id = %d\n", (empLinkedListNO+1), id);
        }else {
            System.out.println("在哈希表中，没有找到雇员");
        }
    }
    //编写散列函数
    public int hashFun(int id) {
        return id % size;
    }
}

//表示一个雇员
class Emp{
    public int id;
    public String name;
    public Emp next;
    public Emp(int id, String name) {
        super();
        this.id = id;
        this.name = name;
    }
}

//创建一个EmpLinkedList
class EmpLinkedList{
    private Emp head;
    public void add(Emp emp) {
        //添加第一个雇员需要判断
        if(head==null) {
            head = emp;
            return;
        }
        Emp curEmp = head;
        while(true) {
            if(curEmp.next==null) {
                break;
            }
            curEmp = curEmp.next;
        }
        curEmp.next = emp;
    }
    public void list(int no) {
        if(head==null) {
            System.out.println("第"+ (no+1) +"条链表为空");
            return; 
        }
        System.out.print("第"+ (no+1) +"条链表信息为：");
        Emp curEmp = head;
        while(true) {
            System.out.printf("=> id =%d name=%s\t",curEmp.id, curEmp.name);
            if(curEmp.next==null) {
                break;
            }
            curEmp = curEmp.next;
        }
        System.out.println();
    }
    //根据id查找
    //找到返回Emp,找不到返回空
    public Emp findEmpById(int id) {
        if(head==null) {
            System.out.println("链表空");
            return null;
        }
        //辅助指针帮忙查找
        Emp curEmp = head;
        while(true) {
            if(curEmp.id==id) {
                break;
            }
            if(curEmp.next==null) {
                curEmp = null;
                break;
            }
            curEmp = curEmp.next;
        }
        return curEmp;
    }
}