哈希表

哈希表（散列表）根据关键码值(Key)直接访问，加快查找的速度。

简单来说就是把数据分组，在进行查找的时候直接在对应的组里进行查找，以此减少查找数据时对不必要查找数据时所浪费的时间

package hashtab;

import java.util.Scanner;

public class HashTabDemo {

    public static void main(String[] args) {
        HashTab hashTab = new HashTab(7);
        String key = "";
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("add");
            System.out.println("list");
            System.out.println("find");
            System.out.println("del");
            System.out.println("exit");
            key = scanner.next();
            switch (key) {
                case "a":
                    int id = scanner.nextInt();
                    String name = scanner.next();
                    Emp emp = new Emp(id, name);
                    hashTab.add(emp);
                    break;
                case "list":
                    hashTab.list();
                    break;
                case "find":
                    id = scanner.nextInt();
                    hashTab.findEmpById(id);
                    break;
                case "d":
                    id = scanner.nextInt();
                    hashTab.deleteById(id);
                    break;
                case "exit":
                    scanner.close();
                    System.exit(0);
                default:
                    break;
            }
        }
    }

}

class HashTab {
    private EmpLinkedList[] empLinkedListArray;
    private int size;

    public HashTab(int size) {
        this.size = size;
        empLinkedListArray = new EmpLinkedList[size];
        for (int i = 0; i < size; i++) {
            empLinkedListArray[i] = new EmpLinkedList();
        }
    }

    public void add(Emp emp) {
        int empLinkedListNO = hashFun(emp.id);
        empLinkedListArray[empLinkedListNO].add(emp);

    }

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

    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 id = %d\n", (empLinkedListNO + 1), id);
        } else {
            System.out.println("no find");
        }
    }

    public void deleteById(int id) {
        int empLinkedListNO = hashFun(id);
        empLinkedListArray[empLinkedListNO].delete(id);
        System.out.println("数据已删除");
        list();
    }

    //编写散列函数(取模法)
    public int hashFun(int id) {
        return id % size;
    }
}

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

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

class EmpLinkedList {
    private Emp head;

    public void add(Emp emp) {
        if (head == null) {
            head = emp;
            return;
        }
        Emp curEmp = head;
        while (true) {
            if (curEmp.next == null) {
                break;
            }
            curEmp = curEmp.next;//后移
        }
        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) + "条链表的信息为");
        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;//后移遍历
        }
        System.out.println();
    }

    public Emp findEmpById(int id) {
        if (head == null) {
            System.out.println("null");
            return null;
        }
        Emp curEmp = head;
        while (true) {
            if (curEmp.id == id) {
                break;
            }
            //退出
            if (curEmp.next == null) {
                curEmp = null;
                break;
            }
            curEmp = curEmp.next;
        }
        return curEmp;
    }

    public void delete(int id) {
        Emp previous = null;
        Emp curEmp = head;
        while (curEmp != null && id != curEmp.id) {
            previous = curEmp;
            curEmp = curEmp.next;
        }
        if (previous == null) {
            head = head.next;
        } else {
            previous.next = curEmp.next;
        }
    }
}

 

来源：https://www.cnblogs.com/bingbug/p/12286706.html