算法与数据结构基础（一）排序基础1.选择排序

一句话概括：循环每次从未排序里选择一个最小或的最大的元素依次放好，直到最后（没有未排序的了）。

1.int型数组选择排序

import java.util.Random;

public class test1 {
	
	private static int a[];

	public static void main(String[] args) {

		produceData(10,1,10);
		print();
		sort();
		print();
		
	}

	//产生数据
	private static void produceData(int n,int min,int max ) {
		
		a = new int[n];
		
		Random random = new Random();
		
		for(int i= 0;i<n ;i++){
			a[i] = random.nextInt(max)%(max-min)+min;
		}
		
		
	}
	//排序
	private static void sort() {

		int n = a.length;
		
		for(int i=0;i<n;i++)
		{
			int minindx = i;
			
			for(int j = i+1;j<n;j++)
			{
				if(a[minindx]>a[j])
					minindx = j;
			}
			
			int tmp =  a[minindx];
			a[minindx] = a[i];
			a[i] = tmp;
			
		}
		
	}

	private static void print() {
		

		int n = a.length;
		
		for(int i=0;i<n;i++)
		{
			System.out.print(a[i]+"--");
		}
		System.out.println();
	}
	
}

2.使用Comparable接口实现各种数据类型排序

自定义的Student类:

import java.util.Comparator;

public class Student implements Comparable<Student>{
	
	public String name;
	public int score;
	
	
	
	public Student(String name, int score) {
		super();
		this.name = name;
		this.score = score;
	}


	public String getName() {
		return name;
	}


	public void setName(String name) {
		this.name = name;
	}


	public int getScore() {
		return score;
	}


	public void setScore(int score) {
		this.score = score;
	}


	@Override
	public String toString() {
		return "Student [name=" + name + ", score=" + score + "]";
	}


	@Override
	public int compareTo(Student o) {
		if(this.getScore()>o.getScore())
			return 1;
		else if(this.getScore()<o.getScore())
			return -1;
		else
			return this.getName().compareTo(o.getName());
	}
	

}

排序算法

import java.util.Comparator;
import java.util.Random;

public class test1 {
	

	public static void main(String[] args) {

		Student[] stus = produceData();
		print(stus);//打印原来顺序
		sort(stus);
		print(stus);
		
		//比较Double类型（也实现了Comparable接口）
		Double[] d = {3.14,3.11,3.99};
		sort(d);
		print(d);
		
	}

	//产生数据
	private static Student[] produceData() {
		
		Student[] stus = new Student[4];
		stus[0] = new Student("A",66);
		stus[1] = new Student("B",90);
		stus[2] = new Student("C",80);
		stus[3] = new Student("D",100);
		
		return stus;
		
	}
	//排序
	private static void sort(Comparable[] arry) {

		int n = arry.length;
		
		for(int i=0;i<n;i++)
		{
			int minindx = i;
			
			for(int j = i+1;j<n;j++)
			{
				if(arry[minindx].compareTo(arry[j])<0)
					minindx = j;
			}
			
			Comparable tmp =  arry[minindx];
			arry[minindx] = arry[i];
			arry[i] = tmp;
			
		}
		
	}

	private static void print(Object[] stus) {
		
		int n = stus.length;
		
		for(int i=0;i<n;i++)
		{
			System.out.print(stus[i]+"--");
		}
		System.out.println();
	}
	
}

3.编写一个类来测试排序算法运行时间(利用反射和系统时间实现)

import java.lang.reflect.Method;

public class SortTestHelper {

	public static void testSort(String sortClassName,Comparable[] arry)
	{
		try {
			
			//告诉类名即可获取class对象
			Class sortClass =  Class.forName(sortClassName);
			//指明方法名和参数列表就可以获取
			//getDeclaredMethod()获取的是类自身声明的所有方法，包含public、protected和private方法。	　　
			//getMethod()获取的是类的所有共有方法，这就包括自身的所有public方法，和从基类继承的、从接口实现的所有public方法。
			Method sortMethod = sortClass.getDeclaredMethod("sort", new Class[]{Comparable[].class});
			Object[] params = new Object[]{arry};
			
			long startTime = System.currentTimeMillis();
			
			//第一个参数是调用哪个对象实例的此方法，静态就写null，第二个为方法参数
			sortMethod.invoke(null, params);
			
			long overTime = System.currentTimeMillis();
			
			System.out.println("耗时："+(overTime-startTime+" ms!"));
			
			judgeSorted(arry);
			
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	private static void judgeSorted(Comparable[] arry) {
		
		for (int i = 0; i < arry.length-1; i++) {
			if(arry[i].compareTo(arry[i+1])<0)
			{
				System.out.println("排序失败!");
				return;
			}
		}
		System.out.println("排序成功!");
		
	}
	
	public static void print(Object[] data) {
		
		int n = data.length;
		
		for(int i=0;i<n;i++)
		{
			System.out.print(data[i]+"--");
		}
		System.out.println();
	}
	
	public static Integer[] generateRandomArray(int n,int min, int max){
		
		assert min>max;
		
		Integer[] data = new Integer[n];
		
		for (int i = 0; i < data.length; i++) {
			data[i] = new Integer((int)(Math.random()*(max-min+1))+min);
		}
		
		return data;
		
	}
	
}