[数据结构与算法]Java实现哈希表

哈希表也叫散列表，是根据关键码值(key-value)而进行直接访问的数据结构。它通过把关键码值映射到表中的某一位置来访问记录，这个映射函数叫做散列函数，存放记录的数组叫散列表。

哈希表可以用数组+链表来实现，也可以用数组+树来实现。本例子用数组+链表来实现。散列函数直接用取余来完成。

public class HashTable {
    private int size;
    private EmpLinkedList[] empLinkedList;

    public static void main(String[] args) {
        HashTable hashTable = new HashTable(8);
        Scanner scanner = new Scanner(System.in);
        String key = "";
        while (true) {
            System.out.println("欢迎使用散列表");
            System.out.println("新增职员：add");
            System.out.println("修改职员：update");
            System.out.println("查询职员：find");
            System.out.println("删除职员：remove");
            System.out.println("遍历职员：list");
            System.out.println("退出散列表：exit");
            key = scanner.next();
            switch (key) {
                case "add": {
                    System.out.println("输入id");
                    int i = scanner.nextInt();
                    System.out.println("输入姓名");
                    String name = scanner.next();
                    Emp emp = new Emp(i, name);
                    hashTable.add(emp);
                    break;
                }
                case "update": {
                    System.out.println("输入id");
                    int i = scanner.nextInt();
                    System.out.println("输入姓名");
                    String name = scanner.next();
                    Emp emp = new Emp(i, name);
                    hashTable.update(emp);
                    break;
                }
                case "find": {
                    System.out.println("输入id");
                    int i = scanner.nextInt();
                    System.out.println(hashTable.findEmyById(i).name);
                    break;
                }
                case "remove": {
                    System.out.println("输入id");
                    int i = scanner.nextInt();
                    hashTable.removeById(i);
                    break;
                }
                case "list": {
                    hashTable.list();
                    break;
                }
                case "exit": {
                    scanner.close();
                    System.exit(0);
                }
            }
        }
    }

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

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

    public Emp findEmyById(int id) {
        return empLinkedList[getHash(id)].findById(id);
    }

    public void removeById(int id) {
        empLinkedList[getHash(id)].removeById(id);
        System.out.println("删除成功,id为：" + id);
    }

    public void update(Emp emp) {
        empLinkedList[getHash(emp.id)].update(emp);
    }

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

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

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

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

class EmpLinkedList {

    private Emp head;

    // 头结点就是第一个节点
    public void add(Emp emp) {
        if (head == null) {
            head = emp;
            return;
        }
        Emp temp = head;
        while (temp.next != null) {
            temp = temp.next;
        }
        temp.next = emp;
    }

    public Emp findById(int id) {
        Emp temp = head;
        if (temp == null) {
            System.out.println("链表为空");
            return null;
        }
        while (true) {
            if (temp.id == id) {
                return temp;
            }
            if (temp.next == null) {
                break;
            }
            temp = temp.next;
        }
        return null;
    }

    public void update(Emp emp) {
        Emp temp = head;
        if (emp == null || temp == null) {
            return;
        }
        while (true) {
            if (temp.id == emp.id) {
                temp.name = emp.name;
                break;
            }
            if (temp.next == null) {
                break;
            }
            temp = temp.next;
        }
    }

    public void removeById(int id) {

        Emp temp = head;
        if (temp == null) {
            return;
        }
        while (temp.next != null) {
            if (temp.next.id == id) {
                temp.next = temp.next.next;
            }
            temp = temp.next;
        }
    }

    public void list() {
        Emp temp = head;
        if (temp == null) {
            return;
        }
        while (true) {
            System.out.println("id=" + temp.id + ",name=" + temp.name);
            if (temp.next == null) {
                break;
            }
            temp = temp.next;
        }
    }
}

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