- See a real demand
google 's a problem on the machine :
There is a company , when a new employee to report the time , requested that the employee's information is added (id, gender , ages , address ..), when the input of the employee id time , requires the employee to find all the information .
Requirements : do not use a database , try to save memory , the faster the better => hash table ( hash )
- Basic introduction hash table
Hash table ( the Hash Table , also called hash table), based on the key code value (Key value) to directly access a data structure. In other words, to access the records by key values are mapped to table a position to speed up the search. This mapping function called a hash function, recording storage array is called a hash table.
- Applications
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google 's a problem on the machine :
There is a company , when a new employee to report the time , requested that the employee's information is added (id, gender , ages , address ..), when the input of the employee id time , requires the employee to find all the information .
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Requirements :
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Without using a database ,, the faster the better => hash table ( hash )
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When you add a guarantee in accordance with id high insertion Low [ after-school thinking: If id is not inserted from low to high, but still requires each linked list from low to high, how to solve ?]
- Implemented using a hash table lists , this list without meter
[ namely : a first node on the list to store employee information ]
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Analysis of ideas and draw schematic
Code implementation [ CRUD ( show all employees, according to id query )]
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Code
package com.atguigu.chapter18.hashtab
import scala.io.StdIn import util.control.Breaks._
object HashTabDemo { def main(args: Array[String]): Unit = { // create HashTab val hashTab = new HashTab(7) // write a simple menu var key = " " while (true) { println ( "add: Add Employees ") println ( "list: display the employee ") println("find: 查找雇员") println("exit: 退出系统")
key = StdIn.readLine() key match { case "add" => { println("输入id") val id = StdIn.readInt() println("输入名字") val name = StdIn.readLine() val emp = new Emp(id, name) hashTab.add(emp) } case "find" => { println("输入要查找的雇员的id") val id = StdIn.readInt() hashTab.findEmpById(id) } case "list" => { hashTab.list() } }
} } }
//创建Emp类 class Emp(eId: Int, eName: String) { val id = eId var name = eName var next: Emp = null }
//创建EmpLinkedList class EmpLinkedList { //定义头指针, 这里head 我们直接回指向一个雇员 var head: Emp = null
//添加雇员方法 //假定，添加的雇员的id是自增的，即雇员分配的id总是从小到大 //找到链表的最后加入即可 def add(emp: Emp): Unit = {
//如果是第一个雇员 if (head == null) { head = emp return } //定义辅助指针 var cur = head
breakable { while (true) { if (cur.next == null) { break() } cur = cur.next } } //这时cur 指向了链表的最后 cur.next = emp
}
//遍历链表的方法 def list(i: Int): Unit = { if (head == null) { println(s"第${i}条链表为空") return }
print(s"第${i}条链表信息为\t") //定义辅助指针 var cur = head breakable { while (true) { if (cur == null) { break() } //输出雇员信息 printf(" => id=%d name=%s\t", cur.id, cur.name) cur = cur.next // } } println() }
//如果有，返回emp ,没有返回null def findEmpById(id: Int): Emp = { //遍历 if (head == null) { println("链表为空，没有数据~~") return null }
var cur = head
breakable { while (true) { if (cur == null) { break() } if (cur.id == id) { break() } cur = cur.next } } return cur } }
//size = 700 class HashTab(val size: Int) { //size 会称为只读属性 val empLinkedListArr: Array[EmpLinkedList] = new Array[EmpLinkedList](size) //初始化我们的empLinkedListArr 的各个元素 for (i <- 0 until size) { empLinkedListArr(i) = new EmpLinkedList }
def add(emp: Emp): Unit = { //返回该员工，应该加入到那条链表 val empLinkedListNo = hashFun(emp.id) empLinkedListArr(empLinkedListNo).add(emp) }
def list(): Unit = { //遍历整个hash表 for (i <- 0 until size) { empLinkedListArr(i).list(i) } }
//编写一个findEmpById def findEmpById(id:Int): Unit = { //返回该员工，应该加入到那条链表 val empLinkedListNo = hashFun(id) val emp = this.empLinkedListArr(empLinkedListNo).findEmpById(id) if (emp!=null) { printf(s"在第 $empLinkedListNo 找到id=%d name=%s\n", id, emp.name) }else{ printf("没有找到id为 %d \n", id) } } //散列函数, 可以定制 def hashFun(id: Int): Int = { id % size } } |
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晚上完成的任务
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能够写出一个hashtab
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解决插入的雇员id 的顺序是从小到大, 而且不能重复