数据结构之哈希表

1.哈希表的基本介绍

哈希表(Hash table)也叫做散列表,是根据关键码值(key value)而直接进行访问的数据结构,也就是说,它通过把关键码映射到表中的一个位置来访问记录,以加快查找的速度,这个映射函数叫做散列函数,存放记录的数组叫做散列表

哈希表实战题
录入员工的信息,当输入员工的id时,查找出该员工
要求:不要使用数据库,越快越好

使用哈希表实现图分析

代码实现:

package com.self.dataStructure.hashTable;

import java.util.Scanner;

public class HashTableDemo {
    public static void main(String[] args) {
        HashTab hashTab = new HashTab(7);

        String key = "";
        Scanner scanner = new Scanner(System.in);
        boolean a = true;
        while (a){
            System.out.println("add:添加");
            System.out.println("show:遍历");
            System.out.println("find:查找");
            System.out.println("exit:退出");
            System.out.println("delete:删除");
            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.addEmp(emp);
                    break;
                case "show":
                    hashTab.showAllList();
                    break;
                case "find":
                    int no = scanner.nextInt();
                    hashTab.findEmpById(no);
                    break;
                case "exit":
                    scanner.close();
                    a = false;
                    System.out.println("program id stop");
                    break;
                case "delete":
                    int number = scanner.nextInt();
                    hashTab.deleteById(number);
                    break;
            }
        }
    }
}
class HashTab{
    private EmpLinkedList[] empLinkedListArray;
    private int size;

    public HashTab(int size) {
        this.empLinkedListArray = new EmpLinkedList[size];
        this.size = size;
        for (int i = 0; i < size; i++) {
            empLinkedListArray[i] = new EmpLinkedList();
        }
    }
    public void addEmp(Emp emp){
        int empLinkedListNO = hashFun(emp.id);
        empLinkedListArray[empLinkedListNO].addEmp(emp);
    }
    public void showAllList(){
        for (int i = 0; i < size; i++) {
            empLinkedListArray[i].sowList(i);
        }
    }
    public void findEmpById(int no){
        int empLinkedListNO = hashFun(no);
        Emp emp = empLinkedListArray[empLinkedListNO].findEmpById(no);
        System.out.println(emp);
    }
    public void deleteById(int no){
        int empLinkedListNO = hashFun(no);
        empLinkedListArray[empLinkedListNO].deleteById(no);
    }
    //散列函数
    public int hashFun(int id){
        return id % size;
    }

}
class Emp{
    public int id;
    public String name;
    public Emp next;  //默认值为null
    public Emp(int id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public String toString() {
        return "Emp{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}
class EmpLinkedList{
    private Emp head;  //头指针,执行第一个Emp,因此我们这个链表的head,是直接指向第一个Emp
    /*添加到雇员链表
    假定添加的雇员id是子增长的,即id的分配总是从小到大,所以将添加的雇员加入到本链表最后即可
    * */
    public void addEmp(Emp emp){
        if(head == null){
            head = emp;
            return;
        }
        Emp curEmp = head;
        while (true){
            if(curEmp.next == null){
                break;
            }
            curEmp = curEmp.next;
        }
        curEmp.next = emp;
    }
    public void sowList(int no){
        if(head == null){
            System.out.println(no+1+"\tcurrent linkedList is null");
            return;
        }
        Emp curEmp = head;
        System.out.println(no+1+"\tcurrent linkedList message is");
        while (true){
            System.out.println(curEmp);
            if(curEmp.next == null){
                break;
            }
            curEmp = curEmp.next;
        }
    }
    public Emp findEmpById(int id){
        if(head == null){
            System.out.println("current linkedList is null");
            return null;
        }
        Emp curEmp = head;
        while (true){
            if(curEmp.id == id){
                break;
            }
            if(curEmp.next == null){
                curEmp = null;
                break;
            }
            curEmp = curEmp.next;
        }
        return curEmp;
    }
    public void deleteById(int id){
        boolean flag = false;
        if(head == null){
            System.out.println("current linkedList is null");
            return ;
        }
        if(head.id == id){
            head = head.next;
            return;
        }
        Emp curEmp = head;
        while (true){
            if(curEmp.next == null){
                break;
            }
            if(curEmp.next.id == id){
                flag = true;
                break;
            }
            curEmp = curEmp.next;
        }
        if(flag){
            curEmp.next = curEmp.next.next;
        }
    }
}