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());
}
}
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;
}
}
