java算法之插入排序

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。

插入排序原理：

     将数组分成两部分，第一部分是有序的，第二部分是无序的。假设数组长度为N，那么把第一个元素当作是有序的第一部分，其他N-1个元素则为第二部分。从第二部分里依次取元素插到第一部分有序数组合适的地方。这样有序部分越来越长，无序部分越来越短，最后就都成有序的了。

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

ackage 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. 插入排序

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);
               //插入排序
               inSertSort(persons);	
	}
	/**
	 * 直接插入排序
	 */
	private static void inSertSort(Person [] persons){
		for(int i = 1;i<persons.length;i++){ 
		    //取第i个元素，插到0->i-1个元素的数组中
		    Person temp = persons[i];
		    
		    for(int j = i-1;j>=0;j--){
		    	if(temp.score>=persons[j].score){
		    		System.out.println("insert "+ temp.score+" to "+(j+1)+" position");
		    		persons[j+1]= temp;
		    		break;
		    	}else{
		    		System.out.println("move "+ persons[j]+" to "+(j+1)+" position");
		    		persons[j+1] = persons[j];
		    		
//		    		System.out.println("position "+ j+" = "+temp);
//		    		persons[j]=temp;
		    	}
		    	
		    	if(j == 0){
		    		persons[j] = temp;
		    	}
		    }
		    afterSort(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();
	}
}

4.排序结果演示

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

insert 82 to 1 position
round 1 sort: 60 [82] 23 31 55 89 92 48 50 23

move 82 to 2 position
move 60 to 1 position
round 2 sort: 23 60 [82] 31 55 89 92 48 50 23

move 82 to 3 position
move 60 to 2 position
insert 31 to 1 position
round 3 sort: 23 31 60 [82] 55 89 92 48 50 23

move 82 to 4 position
move 60 to 3 position
insert 55 to 2 position
round 4 sort: 23 31 55 60 [82] 89 92 48 50 23

insert 89 to 5 position
round 5 sort: 23 31 55 60 82 [89] 92 48 50 23

insert 92 to 6 position
round 6 sort: 23 31 55 60 82 89 [92] 48 50 23

move 92 to 7 position
move 89 to 6 position
move 82 to 5 position
move 60 to 4 position
move 55 to 3 position
insert 48 to 2 position
round 7 sort: 23 31 48 55 60 82 89 [92] 50 23

move 92 to 8 position
move 89 to 7 position
move 82 to 6 position
move 60 to 5 position
move 55 to 4 position
insert 50 to 3 position
round 8 sort: 23 31 48 50 55 60 82 89 [92] 23

move 92 to 9 position
move 89 to 8 position
move 82 to 7 position
move 60 to 6 position
move 55 to 5 position
move 50 to 4 position
move 48 to 3 position
move 31 to 2 position
insert 23 to 1 position
round 9 sort: 23 23 31 48 50 55 60 82 89 [92]

5. 拓展内容