java算法之冒泡排序

Android面试时经常也会被问到数据结构和算法的问题，最近有时间，写点实例。

我模拟的场景是对一个班上学生成绩进行排名。

冒泡排序原理：

       N个元素相邻的两两元素进行比较，如果哪个元素大一些就调换（往上推），最终一轮下来，最大的元素就被推到了最后（就像气泡冒上来了越来越大一样，所以叫冒泡排序）此时第N个元素是最大的。下一轮就从0到N-1的元素里面两两比较，又将最大的元素（小于第N个元素）推到最后。这样不停的进行，最后数组就变成从小到大有序的了。

1.Person.java 实体类

package com.demo.sort;

public class Person {
	
	/**
	 * 名字
	 */
	public String name;
	
	/**
	 * 分数
	 */
	public int score;

	public Person(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;
	}

	public String toString() {
		return ""+score+"";
	}
	
}

2.数据准备

package com.demo.sort;
public class DataUtil {
	Person person1 = new Person("张一",60);
	Person person2 = new Person("张二",82);
	Person person3 = new Person("张三",23);
	Person person4 = new Person("张四",31);
	Person person5 = new Person("张五",55);
	Person person6 = new Person("张六",89);
	Person person7 = new Person("张七",92);
	Person person8 = new Person("张八",48);
	Person person9 = new Person("张九",50);
	Person person10 = new Person("张十",23);
	
	Person [] persons = {
				person1,person2,person3,person4,person5,
				person6,person7,person8,person9,person10
			};
	
	public Person[] getData(){
		return persons;
	}
}

3. 冒泡排序

package com.demo.sort;

/**
 * 冒泡排序
 * @author http://blog.youkuaiyun.com/nnmmbb
 *
 */
public class SortDemo {
	
	public static void main(String args[]){
		
		Person [] persons = new DataUtil().getData();
		beforeSort(persons);		
		//冒泡排序
		BuddleSort(persons);
	}
	
	
	/**
	 * 冒泡排序
	 * 
	 * @param persons
	 */  
	private static void BuddleSort(Person[] persons) {
		for(int i= persons.length-1;i>0;i--){
			for(int j=0;j<i ; j++){
				if(persons[j].score > persons[j+1].score){
					
					System.out.println(persons[j].toString()+" == 调换 == "+ persons[j+1].toString());
					
					Person temp =persons[j];
					persons[j] = persons[j+1];
					persons[j+1] = temp;
				}else{
					System.out.println(persons[j].toString()+" == 不调换 == "+ persons[j+1].toString());
				}
			}
			afterSort(persons.length-i,persons);
			System.out.println();
		}
		
	}
	  
	private static void afterSort(int index,Person[] persons) {
		System.out.print("round " +index+ " sort:");
		for(int i=0;i<persons.length;i++){
			if(i == index){
				System.out.print(" ["+ persons[i].toString() +"]");
			}else{
				System.out.print(" "+persons[i].toString());
			}
		}
		System.out.println();
	}


	private static void beforeSort(Person[] persons) {
		System.out.print("before sort:");
		for(int i=0;i<persons.length;i++){
			System.out.print(" "+persons[i].toString());
		}
		System.out.println();
		System.out.println();
	}


}

3.排序结果演示：

before sort: 60 82 23 31 55 89 92 48 50 23

60 == 不调换== 82
82 == 调换 == 23
82 == 调换 == 31
82 == 调换 == 55
82 == 不调换== 89
89 == 不调换== 92
92 == 调换 == 48
92 == 调换 == 50
92 == 调换 == 23
round 1 sort: 60 [23] 31 55 82 89 48 50 23 92

60 == 调换 == 23
60 == 调换 == 31
60 == 调换 == 55
60 == 不调换== 82
82 == 不调换== 89
89 == 调换 == 48
89 == 调换 == 50
89 == 调换 == 23
round 2 sort: 23 31 [55] 60 82 48 50 23 89 92

23 == 不调换== 31
31 == 不调换== 55
55 == 不调换== 60
60 == 不调换== 82
82 == 调换 == 48
82 == 调换 == 50
82 == 调换 == 23
round 3 sort: 23 31 55 [60] 48 50 23 82 89 92

23 == 不调换== 31
31 == 不调换== 55
55 == 不调换== 60
60 == 调换 == 48
60 == 调换 == 50
60 == 调换 == 23
round 4 sort: 23 31 55 48 [50] 23 60 82 89 92

23 == 不调换== 31
31 == 不调换== 55
55 == 调换 == 48
55 == 调换 == 50
55 == 调换 == 23
round 5 sort: 23 31 48 50 23 [55] 60 82 89 92

23 == 不调换== 31
31 == 不调换== 48
48 == 不调换== 50
50 == 调换 == 23
round 6 sort: 23 31 48 23 50 55 [60] 82 89 92

23 == 不调换== 31
31 == 不调换== 48
48 == 调换 == 23
round 7 sort: 23 31 23 48 50 55 60 [82] 89 92

23 == 不调换== 31
31 == 调换 == 23
round 8 sort: 23 23 31 48 50 55 60 82 [89] 92

23 == 不调换== 23
round 9 sort: 23 23 31 48 50 55 60 82 89 [92]

5.扩展内容